When RadEditor is set with width of 100% switching to Full Screen mode and going back from Full Screen to the initial mode, the content area becomes only few lines high.

The following temporary solution should resolve the layout issue for common scenarios:

<telerik:RadEditor ID="txtComments" runat="server" Width="100%" 
	OnClientCommandExecuted="OnClientCommandExecuted">
</telerik:RadEditor>

<script type="text/javascript">
	function OnClientCommandExecuted(sender, args) {
		if (args.get_commandName() === "ToggleScreenMode") {
			sender.repaint();
		}
	}
</script>