Inconsistent mouse behavior in PIE vs Standalone

Mouse is less responsive in standalone than in PIE. Ex: When reading the mouse position, the position isn't updated as often as when in PIE.

1. Download Attached project
2. Play in standalone
3. Position mouse on one side of the screen then Click and hold Middle Mouse Button (MMB)
4. With MMB held, drag mouse across the screen at a slow constant rate

Result:
The camera does not rotate smoothly with the mouse as it travels across screen.

Expected:
Moving the mouse updates camera position constantly on each frame