So, I just ran into a match where one player's reserve troop count was off. It stayed at its previous highest value, when he obviously shouldn't have any left over, as he had a few territories that weren't at 8. At least one other player observed this, and the value was correctly displayed as zero on the player in question's screen. It also happened to another player, and may in fact have been affecting everyone in the game.
Attached screenshot for reference. I didn't quite catch it same turn, but it shows the gist of it.
It appears that the reserves number in the game never went down for anyone but the local player.