Enhanced Input System + FlushPressedKeys behave questionably together

You can get a repro pretty easily with only BP by debug printing something on an enhanced input action press / release event, and also on debug press / release (e.g. in level script), holding down the key, then unfocusing the window by pressing the Windows key or something, which will call FlushPressedKeys - you'll see the debug release event fires, but the enhanced input event doesn't fire.

1. Open a blueprint character
2. Place a "Debug Key P" node in the character
3. Attach print strings the "Pressed" and "released" pins on this debug node
4. Create an Input Mapping Context
5. Create an Input Action
6. Map the input action in the mapping context to the "P" key, with a "Hold and release" trigger set to a 2 second activation theshold
7. Call Add Input Mapping Context on the character to add this mapping context to them
8. Add a BP listener for the input action, adding a print string to the "Triggered" pin
9. PIE
10. Press P and hold it down
11. Press the Windows key, without letting go of P

Result: The enhanced input action does not trigger, but the debug print strings will both print

Expected: The Enhanced Input action triggers when you press the windows key, even whilst holding down P. When you refocus the window (click into it or alt tab in) you can resume using inputs as normal. 

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