Window Updating

Hello, I’ve got a strange situation.
It goes fine on Windows NT but works incorrectly, for example, on Windows 2000.
My application is dialog based and has some OpenGL (derived from CWnd) windows on it.
After initializing of the dialog all OpenGL window have to start rendering. However at the first time it doesn’t happen. The windows containt something like garbages.
But after the second rendering time they containt properly graphics.
I have tried to give the focus to them, invalidate and so on - unfortunately.
Why it happens? What is it and what I should do?
Tnank you in advance,

Are you doing something like this in PreCreateWindow()?


Most notably, setting the CS_OWNDC…