@Kyno
Would you be willing to ask how this works, since it has now come up.
A reasonable reading would say that there's a 30% chance of gaining mastery whenever you gain a buff, but another reasonable reading is that this can happen **only if you have a debuff before you gain that buff**.
This is pretty crucial, since with, say, the auto buff disks (gain 3 buffs/turn) you gain all the buffs without any chance to gain new debuffs in between. So if the 30% procs on the first buff, all debuffs are cleansed and you have a 0% chance on subsequent buffs to gain mastery (since you no longer have debuffs to cleanse).
I've been wondering for a while now how it's supposed to work, and I'd love a clarification.