Hello,
This is a weird bug, but I have a couple of ideas.
1. Do you by any chance have 2x 1080, or just one?
2. Do you have monitors plugged into other GPUs (like integrated) on your computer? If so, could you unplug those, and let me know if it makes a difference?
3. Does changing your MSAA level, either in FlyInside or in FSX make a difference?
Shoot me an e-mail if you want,
dan@flyinside-fsx.com - I can be a little slow, but I'll look into this bug with you in more detail
Thanks,
Dan