In the interest of Full Disclosure, I should list my full configuration:

Win 8.1 Professional x64
FSX w/Accel Pack and DirectX 10 Preview enabled
nVidia GTX 770 running in Surround mode (three widescreen monitors as a single display with a 4th auxiliary monitor)

It could be  the DirectX 10 contributing to the problem.  I have a well known 738NGX payware that handles this just fine, though, so I'm not inclined to drop back to DX9 anytime soon.