@Drayco: From official forums - Mar18, 2014 update: "An upper limit has been set on the effects of Treasure Hunter. Upper limits of Treasure Hunter including the total of bonuses provided by equipment, atma, and job abilities.
Thief: Treasure Hunter +8 - The limit will be raised to +12 as normal when under the increased Treasure Hunter effects granted through thief autoattacks, Sneak Attack, Trick Attack, and the ranger ability Bounty Shot."