Thank you Richard for your suggestion. Let me explain why I'm not keen to do resize. My application is SDI and therefore as far as I know I cannot resize or move client area. So, I have a sole option to move/size only dockable pane that will fill in the client area as soon as the user release the mouse. What I don't like is Windows will not highlight correctly the place where dockable pane will stick to (only part of client area) and only my code will zoom the pane to fit the client. I hope my explanation is not confusing
Actually I found another solution, not ideal but seams like working. It is to create MDI tabbed app. Since the user can group/regroup different tabs into groups (and therefore view frames) that's what I was looking for. The cons of this way, it's impossible to have vertical and horizontal groupping at the same time. But I can live with it.
Thank you anyway.