How do you alt-tab in an opengl windows program, and not come back to the program to find that the opengl window has moved down halfway through the screen?!?!?
btw, i will register soon… 
I saw this effect in a linux port of one of the NeHe tutorials.
I have never seen it in another program so it should be a bug in that app. OpenGL windows is not different from other windows so you should be able to compare the source with a "good " window app. Also the GLUT sources should show a correct implementation.