Cleared vs. indicated altitude mismatch

[Otto Pylott 4]

I am cleared to FL200, have reached FL200 as indicated on my altimeter, I am above the transition level of FL180 (inside the U.S.) and have therefore switched to standard barometric pressure (29.92), yet P2A repeatedly commands an expedited climb to FL200??? (i.e., the altitude I have already reached). My "Allowed Altitude Variance" is set at the default of 150 ft. I notice that if I climb to ~20,400 ft., P2A stops complaining that I am below my cleared altitude.
Question: Why the discrepancy between my indicated altitude and the altitude at which P2A detects the plane to be? Thanks in advance for any assistance.

Related question: Is there a way, in P2A, to view/request the aircraft's current detected altitude (i.e., the altitude at which P2A thinks the aircraft to be)?

Details: Pilot2ATC v2.5.07, Windows 10, XP10, Aircraft: Carenado Pilatus PC-12

Edited December 27, 2018 by Otto Pylott

[Dave-Pilot2ATC 864]

It's possible that the plane you are flying is not reporting it's altitude to FSUIPC/XPUIPC in the standard manner.

There is currently no reporting of indicated altitude in P2A.  Possible future enhancement.

For now, you might want to set the variance higher....500+ ft.

Edited January 9, 2019 by Dave-Pilot2ATC