The layout of the editor's dialogs break when CSS for Window's lightweight mode are appended. This causes unavailability for the developers to use the lightweight feature of the Window
The RadEditor's dialogs are RadWindow controls and mixing the render mode of one type of control on the same page is not a supported scenario (http://www.telerik.com/help/aspnet-ajax/window-render-modes.html). With the Q3 2014 release, the RadEditor supports Lightweight render mode (http://www.telerik.com/help/aspnet-ajax/editor-render-modes.html). To use a RadWindow with RenderMode set to Lightweight and a RadEditor on the same page should be followed by setting the same configuration to the RadEditor control.