Почему мой DataGridCell отклоняет каждый ввод?

У меня есть два элемента TabItem, каждый из которых содержит DataGrid, и в обоих из них я реализую INotifiyDataErrorInfo. Обе DataGrids питаются ViewModel с базовым классом модели (POCO). В первом TabItem все работает как требуется, но во втором TabItem DataGrid принимает ввод только в проверенных полях/ячейках. другие/непроверенные поля/ячейки позволяют мне вводить данные, но когда ячейки теряют фокус, новые вводимые символы отбрасываются/отклоняются.

Что может быть причиной?

Рабочий TabItem/DataGrid:

<UserControl x:Class = "ConfigTool.Controls.RawTagTabItem"
         xmlns = "http://schemas.microsoft.com/winfx/2006/xaml/presentation"
         xmlns:x = "http://schemas.microsoft.com/winfx/2006/xaml"
         xmlns:mc = "http://schemas.openxmlformats.org/markup-compatibility/2006" 
         xmlns:d = "http://schemas.microsoft.com/expression/blend/2008" 
         xmlns:ct_ctrls = "clr-namespace:ConfigTool.Controls"
         mc:Ignorable = "d" 
         d:DesignHeight = "450" d:DesignWidth = "800">

<Grid>
    <ct_ctrls:CTDataGrid x:Name = "tagsGrid" ItemsSource = "{Binding}" GridLinesVisibility = "Vertical" AlternatingRowBackground = "#C3DDE5" 
                         AutoGenerateColumns = "False" CanUserAddRows = "True" IsReadOnly = "False" 
                         SelectionUnit = "FullRow" SelectionMode = "Extended" BorderThickness = "3" CellEditEnding = "CellEditingEnds" RowStyle = "{StaticResource RawTagDataGridRow}">
        <DataGrid.Columns>
            <DataGridTextColumn x:Name = "TagName" Header = "Tag" Width = "*" 
                                Binding = "{Binding Mode=TwoWay, Path=RawTag.TagName, UpdateSourceTrigger=PropertyChanged, ValidatesOnNotifyDataErrors=True, NotifyOnValidationError=True}"
                                ElementStyle = "{StaticResource ResourceKey=textBlockErrStyle}" />
            <DataGridTextColumn x:Name = "TagCycle" Header = "Cycle" 
                                Binding = "{Binding Mode=TwoWay, Path=RawTag.Cycle, UpdateSourceTrigger=PropertyChanged, ValidatesOnNotifyDataErrors=True, NotifyOnValidationError=True}" 
                                ElementStyle = "{StaticResource ResourceKey=textBlockErrStyle}">
            </DataGridTextColumn>
            <DataGridTextColumn x:Name = "TagSource" Header = "Source" Width = "*" 
                                Binding = "{Binding Mode=TwoWay, Path=RawTag.Source, UpdateSourceTrigger=PropertyChanged, ValidatesOnNotifyDataErrors=True, NotifyOnValidationError=True}"
                                ElementStyle = "{StaticResource ResourceKey=textBlockErrStyle}"/>
            <DataGridTextColumn x:Name = "Unassigned" Header = "unassigned" Width = "*" 
                                Binding = "{Binding Mode=OneWay, Path=RawTag.Unassigned, UpdateSourceTrigger=PropertyChanged, ValidatesOnNotifyDataErrors=False}"
                                ElementStyle = "{StaticResource ResourceKey=textBlockUnassignedStyle}"/>
            <DataGridTemplateColumn x:Name = "editTagColumn" Header = "" CanUserResize = "True" >
                <DataGridTemplateColumn.CellTemplate>
                    <DataTemplate>
                        <WrapPanel>
                            <Button x:Name = "btnTagDelete" Click = "BtnTagDelete_Click" CommandParameter = "{Binding}" Height = "15" Width = "15" Margin = "2">
                                <Button.Content>
                                    <Image Source = "../Resources/delete.png"></Image>
                                </Button.Content>
                            </Button>
                        </WrapPanel>
                    </DataTemplate>
                </DataGridTemplateColumn.CellTemplate>
            </DataGridTemplateColumn>
        </DataGrid.Columns>
    </ct_ctrls:CTDataGrid>
</Grid>

Рабочий TabItem/DataGrid НЕТ:

<UserControl x:Class = "ConfigTool.Controls.RawNotificationTabItem"
         xmlns = "http://schemas.microsoft.com/winfx/2006/xaml/presentation"
         xmlns:x = "http://schemas.microsoft.com/winfx/2006/xaml"
         xmlns:mc = "http://schemas.openxmlformats.org/markup-compatibility/2006" 
         xmlns:d = "http://schemas.microsoft.com/expression/blend/2008" 
         xmlns:ct_ctrls = "clr-namespace:ConfigTool.Controls"
         mc:Ignorable = "d" 
         d:DesignHeight = "450" d:DesignWidth = "800">

<Grid>
    <ct_ctrls:CTDataGrid x:Name = "notificationsGrid" ItemsSource = "{Binding}" GridLinesVisibility = "Vertical" AlternatingRowBackground = "#C3DDE5" 
                         AutoGenerateColumns = "False" CanUserAddRows = "True" IsReadOnly = "False" 
                         SelectionUnit = "FullRow" SelectionMode = "Extended" BorderThickness = "3" CellEditEnding = "CellEditingEnds" RowStyle = "{StaticResource NotificationDataGridRow}">
            <DataGrid.Resources>
            <Style x:Key = "wordWrapStyleView" TargetType = "{x:Type TextBlock}">
                <Setter Property = "TextWrapping" Value = "Wrap"/>
            </Style>
            <Style x:Key = "wordWrapStyleEdit" TargetType = "{x:Type TextBox}">
                <Setter Property = "TextWrapping" Value = "Wrap"/>
            </Style>
        </DataGrid.Resources>

        <DataGrid.Columns>

            <DataGridTemplateColumn Header = "Tag">
                <DataGridTemplateColumn.CellTemplate>
                    <DataTemplate>
                        <Grid>
                            <ct_ctrls:TextWithSuggestionControl x:Name = "test" DataContext = "{Binding}" ItemsSource = "{Binding Path=Tags}" 
                                      Value = "{Binding Path=Notification.TagName, Mode=TwoWay, UpdateSourceTrigger=PropertyChanged}" Append = "False"/>
                        </Grid>
                    </DataTemplate>
                </DataGridTemplateColumn.CellTemplate>
            </DataGridTemplateColumn>

            <DataGridTextColumn Header = "Nid" Binding = "{Binding Mode=TwoWay, Path=Notification.Nid}"/>

            <DataGridCheckBoxColumn Header = "Active" Binding = "{Binding Mode=TwoWay, Path=Notification.IsActive, Converter = {StaticResource StringBoolConverter}}" IsThreeState = "False"/>

            <DataGridTextColumn Header = "Type" Binding = "{Binding Mode=TwoWay, Path=Notification.Type}"/>

            <DataGridTextColumn Header = "Limit" Binding = "{Binding Mode=TwoWay, Path=Notification.Limit}">
                <Validation.ErrorTemplate>
                    <ControlTemplate>
                        <StackPanel>
                            <AdornedElementPlaceholder x:Name = "Limit"/>
                            <TextBlock Text = "{Binding [0].ErrorContent}" Background = "Red"/>
                        </StackPanel>
                    </ControlTemplate>
                </Validation.ErrorTemplate>
            </DataGridTextColumn>

            <DataGridTemplateColumn Header = "Operator">
                <DataGridTemplateColumn.CellTemplate>
                    <DataTemplate>
                        <Grid>
                            <ComboBox x:Name = "notificationOp" DataContext = "{Binding}" ItemsSource = "{Binding Path=Operations}" 
                                          Text = "{Binding Path=Notification.Op}" IsEditable = "False" VerticalAlignment = "Top"
                                          SelectedItem = "{Binding Path=Notification.Op, Mode=TwoWay, UpdateSourceTrigger=PropertyChanged}" >
                            </ComboBox>
                        </Grid>
                    </DataTemplate>
                </DataGridTemplateColumn.CellTemplate>
            </DataGridTemplateColumn>

            <DataGridTextColumn Header = "Text" Binding = "{Binding Mode=TwoWay, Path=Notification.Text}"/>

            <DataGridTextColumn Header = "Deadband" Binding = "{Binding Mode=TwoWay, Path=Notification.Deadband}">
                <DataGridTextColumn.ElementStyle>
                    <Style TargetType = "TextBlock">
                        <Setter Property = "HorizontalAlignment" Value = "Right" />
                    </Style>
                </DataGridTextColumn.ElementStyle>
            </DataGridTextColumn>

            <DataGridTextColumn Header = "Delay" ElementStyle = "{StaticResource ResourceKey=textBlockErrStyle}"
                                Binding = "{Binding Mode=TwoWay, Path=Notification.Delay, UpdateSourceTrigger=PropertyChanged, ValidatesOnNotifyDataErrors=True, NotifyOnValidationError=True}">
                <DataGridTextColumn.CellStyle>
                    <Style >
                        <Setter Property = "FrameworkElement.HorizontalAlignment" Value = "Stretch"/>
                        <Setter Property = "TextBlock.TextAlignment" Value = "Right"/>
                    </Style>
                </DataGridTextColumn.CellStyle>
            </DataGridTextColumn>

            <DataGridTextColumn Header = "Expand" ElementStyle = "{StaticResource ResourceKey=textBlockErrStyle}" 
                                Binding = "{Binding Mode=TwoWay, Path=Notification.Expand, UpdateSourceTrigger=PropertyChanged, ValidatesOnNotifyDataErrors=True, NotifyOnValidationError=True}">
                <DataGridTextColumn.CellStyle>
                    <Style >
                        <Setter Property = "FrameworkElement.HorizontalAlignment" Value = "Stretch"/>
                        <Setter Property = "TextBlock.TextAlignment" Value = "Right"/>
                    </Style>
                </DataGridTextColumn.CellStyle>
            </DataGridTextColumn>

            <DataGridTextColumn Header = "SampleCount" ElementStyle = "{StaticResource ResourceKey=textBlockErrStyle}" 
                                Binding = "{Binding Mode=TwoWay, Path=Notification.SampleCount, UpdateSourceTrigger=PropertyChanged, ValidatesOnNotifyDataErrors=True, NotifyOnValidationError=True}">
                <DataGridTextColumn.CellStyle>
                    <Style >
                        <Setter Property = "FrameworkElement.HorizontalAlignment" Value = "Stretch"/>
                        <Setter Property = "TextBlock.TextAlignment" Value = "Right"/>
                    </Style>
                </DataGridTextColumn.CellStyle>
            </DataGridTextColumn>

            <DataGridTemplateColumn Header = "DetailTemplate">
                <DataGridTemplateColumn.CellTemplate>
                    <DataTemplate>
                        <Grid>
                            <ct_ctrls:TextWithSuggestionControl x:Name = "test" DataContext = "{Binding}" ItemsSource = "{Binding Path=DetailTemplates}" 
                                       Value = "{Binding Path=Notification.DetailTemplate, Mode=TwoWay, UpdateSourceTrigger=PropertyChanged}" Append = "False"/>
                        </Grid>
                    </DataTemplate>
                </DataGridTemplateColumn.CellTemplate>
            </DataGridTemplateColumn>

            <DataGridTemplateColumn Header = "DetailParams" Width = "300" >
                <DataGridTemplateColumn.CellTemplate>
                    <DataTemplate>
                        <Grid>
                            <ct_ctrls:TextWithSuggestionControl x:Name = "test" DataContext = "{Binding}" ItemsSource = "{Binding Path=Tags}" 
                                  Value = "{Binding Path=Notification.DetailParamsString, Mode=TwoWay, UpdateSourceTrigger=PropertyChanged}" Append = "True"/>
                        </Grid>
                    </DataTemplate>
                </DataGridTemplateColumn.CellTemplate>
            </DataGridTemplateColumn>

            <DataGridTextColumn Header = "unassigned" 
                                Binding = "{Binding Mode=OneWay, Path=Notification.Unassigned, ValidatesOnDataErrors=False, NotifyOnValidationError=False}"
                                ElementStyle = "{StaticResource ResourceKey=textBlockUnassignedStyle}"/>

            <DataGridTemplateColumn x:Name = "EditNotificationsColumn" Header = "">
                <DataGridTemplateColumn.CellTemplate>
                    <DataTemplate>
                        <WrapPanel>
                            <Button x:Name = "btnNotificationDelete" Click = "BtnNotificationDelete_Click" Height = "15" Width = "15" Margin = "2">
                                <Image Source = "../Resources/delete.png"></Image>
                            </Button>
                        </WrapPanel>
                    </DataTemplate>
                </DataGridTemplateColumn.CellTemplate>
            </DataGridTemplateColumn>
        </DataGrid.Columns>
    </ct_ctrls:CTDataGrid>
</Grid>

DataGrid заполняются после прочтения файлов CSV ... только пытаюсь изменить (непроверенные) ячейки (которые на самом деле являются DataGridTextColumns и DataGridCheckboxColumns) вызывают проблему.