The initial problem is related with the JS error, because of which the editor's initialization is interrupted.  

You can workaround this by incorporating this piece of code:

<telerik:RadWindow ID="RadWindow1" runat="server" Width="805" Height="450" VisibleOnPageLoad="true">
	<ContentTemplate>
		<telerik:RadEditor runat="server" ID="RadEditor1" Height="200" Width="400" >
		</telerik:RadEditor>
	</ContentTemplate>
</telerik:RadWindow>

<script type="text/javascript">
	var oldCommand = Telerik.Web.UI.RadEditor.prototype.toggleEnhancedEdit;

	Telerik.Web.UI.RadEditor.prototype.toggleEnhancedEdit = function (newValue) {
		if ($telerik.isSafari && typeof (newValue) != "undefined" && false == this.disableContentAreaStylesheet(newValue)) {
			window.setTimeout(Function.createDelegate(this, function () {
				this.disableContentAreaStylesheet(newValue);
			}), 200);
		} else {
			oldCommand.call(this, newValue);

		}
	};
</script>