The magic buildings such as geomancers retreat have always supposed to have had a mana upkeep cost. However, since their introduction, they have not charged this upkeep cost. This appears to have changed, perhaps as recently as yesterday.
I'm not complaining about this change; I had a petition in noting the problem for some time. However, I want to alert players to
review your cities where you have magic buildings to check your mana balance; if you were using all your mana in your geo city on geo spells, you might now have negative mana, for example.
Also, the charge for the magic buildings is not reflected in the town's accounts (Resource Summary page). The number on the resource summary and the resource bar therefore does not match; I am assuming that the number on the resource bar is correct, although I have not specifically tried to track mana accumulation to verify this.