Not a mage specific issue, but the jewelcrafting trinket
Figurine - Twilight Serpent still has a 5 minute cooldown on its use effect in rawr 2.1.9, though 3.0.8 changed it to a 2 minute cooldown. Updating the item cache doesn't fix this automatically.
Specific to mages: as evidenced in
this thread, it appears that if an AB cast procs clearcasting, and abarr is spammed at the end of the AB cast time, due to some sort of delay in the recognition of clearcasting/arcane potency it doesn't get applied to or consumbed by abarr, but instead for the next cast. Is this behaviour recognised by rawr.mage? I haven't tested in a wide variety of conditions, so I'm unsure if latency or other factors have much bearing, but I was able to reproduce the behaviour fairly reliably on a test dummy.