This behavior is working very well with the RenderMode="Lightweight" of the Editor control. As you can see from the following blog post - http://www.telerik.com/blogs/spreadsheet-and-modern-rendering-in-ui-for-asp.net-ajax in the section "What Will Happen With the Classic Rendering? ", we will focus our efforts on the Lightweight rendering and will avoid fixing issues in the Classic rendering. Therefore my advice is to use the Lightweight rendering of the Editor control for this case.