The toolbar doesn't show when its mode is ShowOnFocus and PageTop in IE11

A possible resolution is to attach a function to the editor's "focusin" event, the logic of which is to force the visibility state of the toolbar. You can examine the following example:

<telerik:RadEditor runat="server" ID="RadEditor1" 
	ToolbarMode="ShowOnFocus" OnClientLoad="OnClientLoad">

</telerik:RadEditor>

<script type="text/javascript">
	function OnClientLoad(editor, args) {
		editor.attachEventHandler("focusin", function (e) {
			var toolAdapter = editor.get_toolAdapter();

			setTimeout(function () {
				var isVisible = toolAdapter._toolbarHolder ? toolAdapter._toolbarHolder.isVisible() : false;
				if (!isVisible) {
					toolAdapter._showToolbarHolder(true);
				}
			}, 0)
		});
	}
</script>