I have this problem - for the "M.A.C.O. Elite Commander" accolade, as well. The weird part is that it is only one of my toons (Lissan@nuwok). I have 2 other toons which completed the accolades correctly; and since then, I have gotten the costumes unlocked on those 2 toons.
On the toon with the problem, I tried selling the Mk XII ground set to a vendor and buying it back. While I did hear the "accolade sound" when I bought the items back, no accolade triggered.
I submitted a support ticket and their official response was that this was a bug. Please fix this.
I have had this problem with the rep system was instituted, and I have reported it with a continued ignore message from Cryptic. Personally I put this with bugs Cryptic doesn't feel are important enough to fix category, like disappearing BOFF when entering missions or sector space.