It appears that Ludii cannot tell apart a piece XXX and a piece that contains XXX in it when using (id XXX <Player>), such as King and DragonKing.
Edit: Apparently having the King listed first solves the problem. However, this doesn't excuse the problem being there in the first place.
Edit: Apparently having the King listed first solves the problem. However, this doesn't excuse the problem being there in the first place.