I think this shows everything. Career flight, Cessna 208, 5hrs flight.
ATC is nagging me to "descend to 12,000ft, Mission Steps showing reach and descend…
Altimeter is standard, since above 10,000ft.
(but to be precise, if I set the altimeter to what ATC is giving me, 30.46, all is good).
So the bug apparently is that the standard altimeter is not set above FL100.