This is definitely A Thing at the moment.
I find that if I select a parking spot to start an IFR flight, it’s fine until I select a departure, when it changes back to the runway and I can’t reselect a parking spot till I select Automatic or Direct (I forget which it is without looking).
The workaround seems to be to start the flight without a departure and then add it into the flightplan once I’m in the plane.