i've found a bug with the wizard skill "Desintegration". The arcane power per second is not calculated correctly if I'm using items reducing these costs. These happens in difficulty "Normal" as in "Inferno (4)".
Base AP/s: 18
Helmet with -4 AP/s
Amulet with -5 AP/s
Storm Armor - Power of the storm: -3 AP/s
Total: 6 AP/s
attack speed: 1.94
Arcane power regeneration: 12 (because of Astral Presence)
So the skill should last forever (at least very long because of the recast of Storm Armor) but it lasts only for 24 seconds (134 Arcane power).
I have tested this in town with no other skills active.
If you need more information I'll answer your questions as son as possible.