Lightgun in Nestopia core on windows?

Anyone actually got this working correctly? I have noticed that if you keep the mouse in a small area in the upper left corner (maybe original res size?) the cross hair will move around the complete display area just at a speed not really controllable. Once mouse is out of the area the cursor just stays on right side of screen… Is there a setting somewhere that scales the mouse area to match the screen res or something?

on win7 x64