Damn, coming from the CUDA world, this is quite unexpected. Do you know of any resources on FP in the graphics hardware? I mean do they fit A standard (nvfp, bf, etc?)?
Historically graphics programming has been more concerned with looking good rather than being accurate, and behavior is likely different on each GPU. It's a "hop into the water and learn to swim" kind of thing as far as I'm concerned. You will find errors for things you'll never have thought about and there is hardly any way to brace for it except trying on the go.
E.g. floating point behaviour is only the tip of the iceberg. Every GPU vendor also does mipmapping differently (to balance image quality versus required memory bandwidth).