Why does my mouse cursor lag in windowed mode only??

[system]

My game runs online at around 35-40 fps in a window and the mouse lags wayy behind (I have set a new cursor image) and feels horrible, BUT as soon as I go full screen my fps still reads at 35-40 fps but my mouse is now smooth as a whistle.

Why is this? (and don't tell me my fps counter is wrong...its not)

:)

[unimechanic]

Try disabling vertical synchronization to update the frames faster:

QualitySettings.vSyncCount = 0;