But it seems clear to me that Voldemort made some large mistake that night, because no explanation I've seen for Voldemort willingly stopping his war in 1981 holds any water at all.

Still... one of the very first lessons of Quirrel was about pretending to lose when that gained you more than fighting would.

Granted that Voldemort back then was seen to be winning. But he was winning a war we still don't know his motivations for starting in the first place...

because no explanation I've seen for Voldemort willingly stopping his war in 1981 holds any water at all.

True, no explanation offered so far explains it convincingly, but I don't see the idea that an Avada Kedavra bounced off a baby holding any water either.