QGLWidget maximum size

QGLWidget maximum size

I have a QT application using OpenGL drawing with QGLWidget, on Mac OS. I
developed it on my MBP, and it worked well, then later I tried it on a 30"
screen and realised that there is a window size limit, if I increase the
window size beyond a certain limit, the QGLWidget's content disappears and
only some grayis memory junk is visible.
I removed all the code, so that all the application does now is to put a
full size QGLWidget in the window, and it also has a simple repaint event
setting the background black in each iteration. The issue is still visible
with this simple setup, I can't increase the size, at a limit the black
surface disappears and gots replaced by the memory junk.
Interesting facts:
When I decrease the window size, the GL surface comes back to live again
I have several other GL applications (not QT) running in maximized window,
so the issue is not with the OpenGL driver/video card
It seems that the area of the window (nr of pixels) matters, if I make the
window very wide, it's height will be limited and vica versa, I if the
windoe is maximized in height, the width must be small