Imthatguyhere

Get on that Pixel-Grid train or use some better safezone logic to make it all more friendly to the alternate aspect ratio players (no more stretch).

Swapping from Windowed Borderless to Fullscreen should resolve this. It's an issue with Arma not locking your mouse to your main screen. If you love Borderless and want to keep using it and get rid of this, you can use third party tools like Dual Monitor Tools: http://dualmonitortool.sourceforge.net/dmt_cursor.html That will allow you to use a hotkey to lock the cursor to your main monitor.