Ha, finally! I have the same problem (it works the first time, but not when I try again) - and Tom has been totally unable to reproduce it. We compared all of our scripts (byte count), I sent him videos, we screenshared...it doesn´t happen on his system.
So thanks for confirming I am not crazy!
We will certainly keep investigating. Maybe some crazy peripheral interfering (I run a full HOTAS thrustmaster setup)...
For now I just pretend the ground power source is bad and is missing a pin or something...I can live with the GEN bus off (transfer bus still works), until I start the APU.
AND it only happens after some other source has powered the bus (I call it the bus-virginity-problem)...
Cheers, Jan