Is there any known problem concerning the ‘GLint x’ parameter passed to glCopyTexImage2D() ?

I’m trying to extract a 512x512 texture from the frame buffer. I know the image is where I want it, I know I’m providing the correct (x, y) coords to specify the bottom left corner of that image area, but the Copy I get is always displaced in the X-direction.
The Y-Coord is fine and works as expected.

Any ideas please?

Well, don’t know quite what you mean by ‘displaced’, but first thing that comes to mind is glPixelTransfer