exchange of a destroyed powder house

I play with Samael a game called 'game4'. This is what happened during round 12:

Samael sacrifices the Powderhouse to destroy a School of Magic of eran oren
Samael pays 2 gold and exchanges a Prison of eran oren for his or her Powderhouse.

This seems like a bug.

I don't read Spanish, but this seems that Martinez reported the same bug a couple of weeks ago.