The floating toolbars do not appear properly with the new RadWindow Lightweight rendermode. They are too short, backgrounds are missing and sizes are incorrect, so buttons are misaligned and/or overlapping.

A workaround is avoiding the lightweight rendermode of RadWindow through the web.config. Add the following in the <appSettings>:
*<add key="Telerik.Web.UI.RenderMode" value="Lightweight" />*

and other RadWindows that need LightWeight rendering (but they must not be on the same page, or masterPage-contentPage-userControl combination) can have their own RenderMode property set to Lightweight.