When I play Minecraft in windowed mode and it fills the whole screen, kinda like Windowed-Fullscreen(maximized) I get shuttering and the fps is going around 300 as normal but it feels more like 25-30fps. I tried lowering fpscap in the latest snapshot and after 20-30fps I couldnt see any increase in fps.

I have completely normal fps when I have a smaller window than my full resolution and that goes for the Fullscreen option in-game too.

I tried with resizing the window to be almost as big as maximized And bigger than my first screen but still same smooth fps. I have only noticed this problem right now in minecraft and not in any other game of mine. I see this problem going as far as to 1.0.

Edit: I seem to have pin-pointed the problem to be aero, if I disable aero the problem disappears, and it seems that only when aero is on and I have the window either next to or behind the taskbar it starts to shutter. I have no idea why or how it does that but atleast I found whats causing it..

I know that my system specs are more than sufficent and I have checked that the processor, RAM, GPU and HDD arent even used at the most.

(I cannot really show this in a screenshot since the fps is normal and all but it isnt on screen)

I finally after a few hours of searching found that on the launcher itself "disable desktop composition" under the Compability tab fixes the issue fully. Im not sure what exactly it does but I think it is worth mentioning this in some FAQ or wiki for those with the same problem.