This bug still occurs in 1.8.7. Is there a chance this will be fixed for 1.9? I often have Minecraft open in windowed mode on my external while doing other things on my main screen (esp if I'm using an AFK farm), but this mouse bug makes it unplayable unless I move it back to my primary screen
1.8.7 + OptiFine
Macbook Pro 15" Late-2013
Yosemite (10.10.5)
External DVI Display
Just got the chance to use my external screen setup on Vanilla 1.8.8 and the bug is definitely replicable on my Mac. It seems that the mouse appears a set number of pixels below center in windowed mode. The external monitor I'm using is 1900x1200 and (I'm estimating) when the window is shorter then 600 pixels the cursor appears outside the window when opening a GUI. For some reason it's not adjusting the cursor placement to the height of the window.