In my application Im using offscreen rendering in a Pbuffer for rendering images files of the scene. Reading the Pbuffer content (using glReadPixels()) I get some invalid colored pixels near the upper left and the lower right corner of the rectangle. But this effect occurres only for selected viewport dimensions (e.g. 720x576 and 100x100 pixels is ok, but 400x230 pixels will fail. NVidia GeforceFX5900 used.
This is funny, and I don’t have a real answer. , but if it’s windows and in a windowed mode, try clipping regions to see what happens. otherwise, the basic rendering interface does this when rendering.
I had the same problem a few months ago. The applications i’m writing have DV resolution as input (720x576). At certain subsample levels my textures were completely messed up and I had no idea why. The only way I could slve it was by using POTD textures and POTD viewport.
Originally I also used texture rectangles to support NPOTD textures, so maybe the bug could have been there.