I have a monitor which does not provide any mode information, and only runs at 640x480. It only functions correctly at 60 Hz, but the default that the nvidia driver jumps to is 75 Hz. That's not really your problem. The problem I have is that when returning from fullscreen in minecraft, it does not preserve the original refresh rate. It instead aims for the "default" for the card.
It's probably a simple enough fix, since you just need to preserve and reset one more variable. It would make my life a bit easier, though.
Duplicate of MC-36746 - If you have not, please use the search function in the future, to see if your bug has already been submitted. If you could not find the original report, please comment with the keywords you searched for.