I discovered that the overlay problem I reported earlier was caused by the Desktop Window Manager, which is responsible for compositing under Vista. The DWM expects applications to draw themselves into an off-screen surface, which it can use for compositing. The solution I found back then, which is to retrieve the DC on the primary surface, caused the locking of the primary surface, which forces the DWM to relieve control to the application and switch back to “Aero Basic” for the duration of the application.
So I came up with a more explicit solution this time:
