Mushroom Prime Minster card bug

Describe the problem. Be as specific as possible!:
He has his own set of monster cards, even though he can only be fought one. This makes it impossible to obtain all 5 cards.

 Images of problem

None, due to the fact I can't screen shot that when you re-enter the map you can't re fight him.

Apparently, you can fight him, exit the map without clearing the quest, retry. Saw it somewhere.