> Can this vsync issue occur if you don't use vsync? > > P.S.: I guess not but what if I'm wrong.
It shouldn't happen if you're not setting vsync. But graphics drivers can force vsync too, and it's possible that they are and you don't know it. That's why I'm suggesting that you enable the little OSD by pressing f11 so you can see if you're at 100% or at 99% or 101% or something.