mybirthdaysoon: One of the earlier posts implied that maybe I entered one of my tournaments as a pawn before upgrading to a knight and entering another tournament. That might have happened and tricked the check.

As luck would have it, I'm waiting for the next round to start in both the tournaments I'm already playing. So I can't easily resign my way out - and I'm reluctant to do so after playing to get there. :)

So I'm probably faced with upgrading to rook to be in the new tournament. But thanks to everyone for clarifying that the restriction does apply to this situation.