I'm not sure if this bug was introduced today with the incremental patch or if it has existed for a while, but Magicka Controller (Mages Guild passive) is broken. Here's what I've noticed so far:

Slotting a MG skill on the front bar increases regen but NOT max mag or damage on that bar. However, it erroneously applies the max mag + damage increase to the back/other bar.

PSA for any players who might want to change up your build. Judging by the Orc passive fiasco I doubt this will be getting fixed this year.