All Telerik .NET tools and Kendo UI JavaScript components in one package. Now enhanced with:
This behavior is caused by the fact that the RadMenu's z-index is bigger than the RadWindow. Try setting the higher z-index value for RadWindow than RadMenu in order to show window above. Check out the following links that might help in this
You can find a more detailed KB article below: Show RadWindow above RadMenu Controlling absolute positioning with z-index.