The described issue is because of the "Zero width nbsp" character, which is not stripped when the text is submitted. Possible resolution is to strip the character with custom function attached to the OnClientSubmit event of the RadEditor control: <telerik:RadEditor runat="server" ID="RadEditor1" OnClientSubmit="OnClientSubmit" /> <script type="text/javascript"> function OnClientSubmit(editor, args) { var html = editor.get_html(true); html = html.replace(/\u200b/g, ""); editor.set_html(html); } </script>