Quote Originally Posted by mancunian
Yes as i said earlier Windows Media Player continues to play video while being dragged as do most other non-Microsoft players. Don't know how they manage it
Easy. You never grab the window frame, but a panel within the frame (an imitation window frame if you will) that permits a drag while rendering.

Otherwise, if you use a standard window all I can say is "Tough luck", because it's a Microsoft-ism. You'll have to ask them why they did it that way.