Native browser behavior is vendor specific and the above issue cannot be replicated with the latest version. Default browser in latest Android versions is Chrome and we recommend using it instead of the older native browser

When the control is modal it should create a second iframe behind the modal background like it creates one behind the popup itself. This will allow the modal background to stay above heavy-weight objects in IE as well.

When a RadEditor or SPRadEditor in a custom WebPart for SharePoint 2013 is placed in an UpdatePanel or RadAjaxPanel it is not ajaxified and loses its content after a post back.

The issue can be workarounded by calling preventDefault of the mousedown event when ComboBox item is clicked:
<telerik:RadScriptManager runat="server" />
<script>
	var onDocumentClick = Telerik.Web.UI.RadComboBox.prototype._onDocumentClick;
	Telerik.Web.UI.RadComboBox.prototype._onDocumentClick = function (e) {
		if (!e) e = event;

		var target = e.target || e.srcElement;

		while (target.nodeType !== 9) {
			if (!target.parentNode || target == this.get_element() || target == this.get_dropDownElement()) {
				e.preventDefault();
				return;
			}

			target = target.parentNode;
		}
		onDocumentClick.call(this, e);
	};
</script>

<telerik:RadComboBox ID="RadComboBox1" runat="server" RenderMode="Lightweight" OnClientBlur="OnClientBlur"
	CheckBoxes="true">
	<Items>
		<telerik:RadComboBoxItem Text="Item1" Value="1" />
		<telerik:RadComboBoxItem Text="Item2" Value="2" />
		<telerik:RadComboBoxItem Text="Item3" Value="3" />
		<telerik:RadComboBoxItem Text="Item4" Value="4" />
	</Items>
</telerik:RadComboBox>

<script>
	function OnClientBlur(sender, args) {
		console.log("Blur event");
	}
</script>