I'd love to help you out. I don't see anything wrong with your code. It would be helpful if you could show me also the RadDockZone and RadDocklayout code you are using.
Are you using update panels, and if so, how and where ?
One thing you could try in the mean time is the following:
|dock.CommandsAutoPostBack = false; |
Please let me know how things go and if you need any further assistance.