Board Game Arena

I noticed that in BGA games, cards like Grand Mufti, which can perform the Behead action on a card with a bishop, are removed from the game after executing this action. Is this a bug in the game, or does it come from some rule (I couldn't find it anywhere)? I'm a relatively new player and have only played a few games, so maybe I missed something in the Living Rules.

It depends which card are you beaheading. If you beahead king you will lose Mufti but if you beahead other cards you will keep it.