You are the first to report such a problem and that is why I will need more information in order to be able to help you. First of all, are the RadSplitter controls duplicated or rather the hidden RadSlidingPanes are visible just beneath the RadSplitter. Are you using a custom skin - in case you do, so you reproduce the problem with a built-in skin as well? Which was the exact version of the suite that you used to create the project and to which did you revert? Could you post here the definition of a RadSplitter that demonstrates the problem?
the Telerik team