The previous versions of the RadDock control used the drag and drop functionality which is provided by the ASP.Net Ajax framework. However, there were a number of performance as well as cross-browser problems with the MS implementation. In the official release of the control from Q2 2008 the drag/drop functionality has been replaced by a brand new improved (Telerik) implementation which addresses the previously existing problems. The new implementation, however, led to the problem you mention in the RadDock control and we are aware of it.
For the moment, we have not received other requests for this feature - you are the first who is asking for it.
Do you really use this functionality? Is it crucial for your scenario? If we receive other requests for this feature we can consider reworking the new drag/drop implementation in order to support it, however, for the moment we accept that this functionality is not used by our customers and therefore we think to remove this example at all.
All the best,
the Telerik team
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