I just hope the engineers get properly briefed.
I once walked out to a Blackhawk for an airtest. There was no-one at the aircraft, the ramp was deserted, but the APU was running!
We shut it down before doing our walkround checks.
The engineer "in charge" then came out and indignantly asked us why! He said the APU was safe to leave running as it said in the Flight Manual there was an automatic system to shut it down if there was a fault.
We agreed that the APU should shut down if there was an oil over-temp or pressure fail.
However! I asked him what he thought would happen if the APU caught fire. He was last seen slapping himself on the forehead.....