Непоследовательное поведение CSS для пользовательской подсказки JavaScript

function togglePopup(element, onoff) {
    var popup = document.getElementById(element.id + "_popup");
    if (popup) {
        if (onoff) {
            popup.classList.add("show");
        }
        else {
            popup.classList.remove("show");
        }
    }
}

.popup {
    position: relative;
    display: inline-block;
    cursor: pointer;
    -webkit-user-select: none;
    -moz-user-select: none;
    -ms-user-select: none;
    user-select: none;
}

/* The actual popup */
.popup .popuptext {
    visibility: hidden;
    width: 160px;
    background-color: #555;
    color: #fff;
    text-align: center;
    border-radius: 6px;
    padding: 8px 8px 8px 8px;
    position: absolute;
    z-index: 1;
    bottom: 125%;
    left: 50%;
    margin-left: -80px;
}

/* Popup arrow */
.popup .popuptext::after {
    content: "";
    position: absolute;
    top: 100%;
    left: 50%;
    margin-left: -5px;
    border-width: 5px;
    border-style: solid;
    border-color: #555 transparent transparent transparent;
}

/* Toggle this class - hide and show the popup */
.popup .show {
    visibility: visible;
    -webkit-animation: fadeIn 1s;
    animation: fadeIn 1s;
}

/* Add animation (fade in the popup) */
@-webkit-keyframes fadeIn {
    from {
        opacity: 0;
    }

    to {
        opacity: 1;
    }
}

@keyframes fadeIn {
    from {
        opacity: 0;
    }

    to {
        opacity: 1;
    }
}

<br><br>
<table class = "shop_table shop_table_responsive cart woocommerce-cart-form__contents" cellspacing = "0">
   <tbody>
      <tr class = "woocommerce-cart-form__cart-item cart_item">
         <td class = "product-remove">
            <div class = "popup" onmouseover = "togglePopup(this, true);" onmouseout = "togglePopup(this, false);" id = "addon_remove_link">
               <label class = "remove">&times;</label>
               <span class = "popuptext" id = "addon_remove_link_popup">To remove add-on items, you must remove associated products</span>
            </div>
         </td>
         <td class = "product-quantity" data-title = "Quantity">
            <div class = "quantity popup" onmouseover = "togglePopup(this, true);" onmouseout = "togglePopup(this, false);" id = "addon_quantity">
               <label class = "screen-reader-text" for = "quantity_6658f8f611307">Thread - GutermannMatching thread for selected items quantity</label>
               <input readonly type = "number" id = "quantity_6658f8f611307" class = "input-text qty text" name = "cart[8f818faae39eca624255ff021f2f2afb][qty]" value = "1" aria-label = "Product quantity" size = "4" min = "0" max = "100" step = "1" placeholder = "" inputmode = "" autocomplete = "off" />
               <span class = "popuptext" id = "addon_quantity_popup">To change add-on quantities, you must add/remove associated products</span>
            </div>
         </td>
      </tr>
   </tbody>
</table>