I logged on to my druid to check - ferals do deal reduced damage while disarmed, they do however still have access to all their abilities - and their stats (apart from weapon damage) don't decrease - so all abilities that are unaffected by weapon damage (ie. Mangle, Shred, Ravage) still work as though the disarm never happened. So my guess is this happened when they shifted you over to weapon damage multipliers for your attacks - because up until then disarms were yet another cc you were immune to ;p
It's cool though, I'll be sure to start disarming ferals more often now! >
Weapon DPS is about x5 more effective at DPS than mastery (best secondary stat). It's still a pretty big hit to anything other than bleeds.