Thanks for bringing this up, Pano! As of the 2.3 content patch, there's currently an issue with Transmutation Mastery by which the percentage chance to receive additional results from transmutations — aside from Transmute: Primal Might — is lower than the intended value. This is likely contributing to the dearth of procs you've observed, and I'd like to offer my apologies for any consternation that has arisen as a result of the discrepancy. I'm happy to report that this matter should be resolved in a future patch, but your continued patience in the interim is appreciated. :)
[ http://forums.worldofwarcraft.com/thread.html?topicId=3547795433&sid=1