I am afraid that I can not reproduce the issue you described. We have seen a similar issue with RadTreeView when the application is running through remote desktop but have not been able to find the exact cause. If you are not using Remote Desktop please send a sample application which demonstrates the issue so that I can debug it and provide a solution if such is available.
Another reason for the described issue can be outdated video drivers or video card issues. We had clients reporting such behavior and they claimed that the issue went away once they updated their video card drivers.
the Telerik team