Discovered check promotion

A few days ago I played a game of chess with my father, quite a turbulent game, and he's still grumpy about it. Anyways, at some point the following position occured (I play black):



With white to move. He was in a lost position, but he made the move
1. Kxd4? which allows a nice little trick:
1. ...a2!
2. Bxa2 b1Q+ 0-1

Anyone ever encountered something strange like this?

In a 3 0 game on ICC, I stumbled into



I played d8 and chose a bishop for the art.