AMD/ATI Pixel Clock Patcher

[ToastyX]

That happens if you reduce the vertical total because there isn't enough time to change the memory clock without screen corruption. It will clock down properly if you use the "Best for LCD" timing, but your monitor can't seem to handle 120 Hz that way. You could add 100 Hz as a secondary detailed resolution and use that for desktop use.

That also happens if you're using multiple monitors. In that case, there's no workaround because the memory clock needs to change during the blanking period of both monitors to avoid screen corruption, but there's no way to guarantee both monitors will refresh at the same time.