According to current implementation of paste functionality for IE, the editor gets the pasted content by executing the browser's paste command - 
editor.get_document().execCommand("Paste", null); 
This does not paste anything when browser's security setting "Allow Programmatic clipboard access" is disabled.

The selected image in SharePoint RadEditor's Image Manager dialog is not displayed when edited in the Image Editor in IE when the property ImageManagerViewMode of the editor is set to Grid.

In the meantime, use the following workaround:

<script type="text/javascript">
                var designMode = Telerik.Web.UI.EditModes.Design;
                var editorPrototype = Telerik.Web.UI.RadEditor.prototype;
                var keypress = editorPrototype._keyPressHandler;
                editorPrototype._keyPressHandler = function (ev) {
                    if (this.get_mode() == designMode) {
                        keypress.call(this, ev);
                    }
                }
                var keyDownOverride = editorPrototype._keyDownHandlerEnableTrackChangesOverride;
                editorPrototype._keyDownHandlerEnableTrackChangesOverride = function (ev) {
                    if (this.get_mode() == designMode) {
                        keyDownOverride.call(this, ev);
                    }
                }
                var keydown = editorPrototype._keyDownHandler;
                editorPrototype._keyDownHandler = function (ev) {
                    if (this.get_mode() == designMode) {
                        keydown.call(this, ev);
                    }
                }
            </script>

For the time being you can manually set the localization string for the "Add Custom Color" and "Current Color" buttons: 
		<telerik:RadEditor ID="RadEditor1" runat="server" RenderMode="Mobile" Language="de-DE" LocalizationPath="~/App_GlobalResources"></telerik:RadEditor>
		<script>
			var initialize = Telerik.Web.UI.Editor.MobileColorPicker.prototype.initialize;
			var addCustomColorTextLocalized = "Add Custom Color Localized";
			var currentColorTextLocalized = "Current Color Localized";

			Telerik.Web.UI.Editor.MobileColorPicker.prototype.initialize = function () {
				var colorPicker = this;
				initialize.call(colorPicker);
				
				colorPicker._addCustomColorText = addCustomColorTextLocalized;
				colorPicker._currentColorText = currentColorTextLocalized;
			}
		</script>

This issue happens only under IE11 with IE9 compatibility mode. Using real IE9 browser the area is rendered correctly.

You should be aware of this issue when testing cross browser functionality of the RadEditor. 

When a table is inserted above a list element and modified via the Table Wizard dialog, it is getting appended as a list item. 

Since upgrading to Q1 2013, any export to csv file type from RadGrid displays an empty space when a column is empty.  It should just be blank.

The links in Preview mode should not be opened at all or at least opened automatically in a new window, so that user could preserve its content.

Possible resolution is to invoke the setTargetsForPreview method on the OnClientLoad event of the editor:

<telerik:RadEditor runat="server" ID="RadEditor1"
	 EditModes="Preview" OnClientLoad="OnClientLoad">
	<Content>
		<a href="http://www.telerik.com">Link</a>
	</Content>
</telerik:RadEditor>

<script type="text/javascript">
	function OnClientLoad(editor, args) {
		Telerik.Web.UI.Editor.Utils.setTargetsForPreview(editor);
	}
</script>

Navigate to:

http://localdemos.telerik.com/aspnet-ajax/treelist/examples/databinding/loadondemand/defaultcs.aspx

1) Expand item with ID:2, then items: id:1413, id:1414

2)Expand item id:1

3)Fill Item ID textbox with "303" and Level textbox with "2"

4)Click "ExpandItemToLevel"

5)The icon of item 304 seems like "expanded"(and it should be), however the item is not expanded.

RadScheduler's "today" link is positioned below the Prev/Next arrows in Safari on iOS and OS X.
It is positioned properly after changing the views.

As a quick fix, you can set CSS:
    <style type="text/css">
        html .RadScheduler .rsHeader > p {
            width: 80px;
        }
    </style>

Width value will vary depending on the skin used.