The module that performed the dragging of RadDock was changed since the version you previously used in order to improve the behavior of the control. The functionality you mentioned, however, is still not implemented in the new module.
I am afraid that there is not a workaround that I can suggest to bring back the old behavior. I have logged a feature request for this functionality so that you can vote for it, comment it and follow its status: http://feedback.telerik.com/Project/108/Feedback/Details/118853
. If it becomes popular we will consider implementing it.
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