Just found this problem with page flipping in directdraw. The directdraw has done such a good job of kicking windows of the screen that with the flip method, message boxes do not always show up. This includes the messageboxes where u set the MB_ICONERROR | MB_SYSTEMMODAL, assertions and even the End task dialog from Ctrl Alt Esc. They show out about half the time.
I notice in Starcraft, the end task dialog shows up always so makes me wonder if they are using page flipping or not? Can anyone use page flipping yet enabling the Ctrl Alt Esc to come out? If not, I'm sticking to off screen buffer.