I have prepared simple application that illustrates Drag and Drop within Child Window opened from child window. However, it seem to work correctly. Could you please look at the attachment. If it does not help would it be possible to share with us some additional information about the scenario in which you are experiencing the problem.
the Telerik team
Do you want to have your say when we set our development plans?
Do you want to know when a feature you care about is added or when a bug fixed?
Telerik Public Issue Tracking
system and vote to affect the priority of the items