I may be wrong, but I think you need to jump hoops to get GRUB to recognise your mouse (Wikipedia
implies you can, I've never seen it done)
So unless you can normally use the mouse in your GRUB setup, I feel it's unlikely that changing anything to do with GRUB will fix this problem. And when you said "possible solution is disabling any input for grub", I assume you mean just mouse input? Or am I missing something here?