We've been trying to reproduce the issue for a while, but never managed to reproduce the 1-line output. However, there definitely seems to be a bug somewhere in the driver affecting this mode on C51 GPUs. If you're affected by this problem (trying to set a 1280x1024 mode on GeForce 61xx/C51 resulting in truncated output), would it be possible for you to answer these questions:
- What is the reference of the screen you're using when the problem happens? If other systems with the same GPU/drivers work fine, what screen are they using?
- Is your screen connected using VGA or DVI? If you have access to the other kind of cable/connector, can you try switching; if so, does it solve/affect the problem?