This problem was fixed in RadEditor for MOSS 5.5.1. The current version of the controls for MOSS is 5.8.1 and 6.0.0 for SP2010. If you are experiencing any problems in SP2010, could you provide us with some additional information? A step by step scenario of how to reproduce it or even a small video where we can actually see the issue will be of great help.
the Telerik team
Check out Telerik Trainer
, the state of the art learning tool for Telerik products.