Sorry, I misunderstood that thread. I thought he was referring to the AMA Safety Code.

According to the rules at http://www.rccombat.com:
Rule 3.3 of the RCCA Open Combat rules states a requirement for engine shutoff.
Rule 3.5 of the RCCA Scale Combat rules states a requirement for engine shutoff.

Of course, it's up to the contest director's discretion whether he wants to enforce that rule or not. If you only have a few competitors at a meet, you really can't afford to be disqualifying people for a minor infraction.

The rule really doesn't make sense, because if you don't have control of the airplane, you almost certainly won't have control to shut off the engine.

The AMA Safety Code does NOT have a requirement for engine shutoff. Of course, if it did, it would have to apply to R/C only. Sorry for the misunderstanding.