I noticed after updating to the version below that the Focus Magic Mage buff is acting like a debuff. It even shows where debuffs are typically listed.
The change occurred between March 23rd and April 14th, I have not reviewed every commit in that time frame to identify exactly when and how the change happened.
I am continuing to investigate but that I would enlist the help of others in case someone else runs into this same issue.
Version Info:
TrinityCore rev. 4a40b8ed4358 2017-04-14 16:53:59 -0300 (3.3.5 branch) (Win64, Release, Static)
TDB 335.62