Some users experience inaccurate mouse input, noting that when clicking on the mouse the actual input is a small margin away from the actual mouse pointer.
To resolve this, please make sure the that application is properly full-screened within the session window.
You do this by clicking on the 'Full screen/Windowed' button until it's the full size of the window (Note that you may need to click it twice; once to make it a window, and then again to make it full screen again):
Once the window is back in full screen mode, you will see accurate mouse input is restored.