To add to the discussion/nightmare 😮
I'm also "trying" to determine the PAUSE states offset x264 (given the Active Pause can't be detected) and discovered the following, not sure if it's with FSUIPC or an Asobo problem, I'm guessing the latter;
Using the "P" keyboard pause, the value returned is 2 and this clears down to 0 when the Ctrl-"P" is seen. You get a "pause" and "un-pause" as expected.
Using the ESC-style pause, heading to the menus, the value returned is 4 and this clears down to 0 when the second ESC is seen. You get a "pause" and "un-pause" as expected.
So far, so good...
If you - in EITHER ORDER - use the "P" to pause and THEN use ESC to head to the menus, the value returned is 6, all well and good, HOWEVER, reversing either pause state in either order NEVER changes the value to 0 it remains at 6 "forever", until you return to the main menu and restart a flight. You do get a "pause"/"un-pause" in the sim but the value is stuck!
Tried in both the C170 and A320...
This is also for an ACARS-style program "BAVACARS", attempting to recognize pauses in flight, which we time-limit.
For now I'm using a position vs. speed, poor second choice method, to determine it, but at least THAT does handle the "Active Pause" into the bargain.
Not sure if this helps, if it's an FSUIPC issue or needs to pass to Asobo...