I would like to ask you clarify a little bit the issue you experience. What do you mean under "the dock beneath"?
Is this another dock different from the one you move? How its position is changed? Do you change it with code?
If you want to fire the DockPositionChanged server-side event when moving a dock make sure that you have set its AutoPostback property to true. Please, refer to the the DockPositionChanged help article
for detailed information when this event gets fired. Information about the corresponding client-side event you can find in the OnClientDockPositionChanged help article
In case the above suggestions cannnot help you solve the issue, please, send us a simple running application which reproduces the problem so that we can test it locally and research the problem. You will need to open a support ticket in order to have the right to attach files. Please, download a trial version of the RadControls for ASP.NET AJAX suite and you will have the right to open a support ticket. For your convenience I have attached a screenshot with instructions how to open a support ticket.
the Telerik team