This is on osx, btw. After using any ability that uses mana, the thaumaturgic tap buff icon remains, but the skill does not give any more mana. I have no idea whether this is intended or not since there's no mention of it in the ability. I dislike it right now since i'm trying to do the mathematics buff and then refill mana with thaumaturgic tap, which requires waiting another 10 turns to refill mana after casting it.
If you are running 10.8 if is possible (due to a bug) that positive buffs like healing stuff and the tap can be resisted by the character. Therefor the buff and cooldown my appear, yet the effect does not. Update to 1.0.9 and try the special teleporthotfix if your 1.0.8 save does not work due to teleportglitches
Thanks for the info, but this is not a resist issue. This is consistent and reproducible. It gives the mana until a mana-using ability is used. Maybe i should have put this in the bugs forum, but i wasn't sure if it was intended.