I will give you very simple logic mj, This is not RO2 Sea, this RO2 us server! got it? And it already happened before, and they fixed it. I have nothing to explain to you. If you want Ninja(3) with stats, go to RO2 SEA and play.
And you dont get the point, how about the very expensive stated tuxedo/wedding dress? If the Ninja costume is have a better stats? Tsk tsk,
And I will give you a simple answer. NA is just a copy of SEA. Deal with it. Therefore its not a bug. Tuxedo/Wedding dress have better stats (+10 stat, 30% drop rate, 12.5% matk/atk power) but these are temporary. Ninja stats are permanent (Stat+12). If you cant comprehend that. You're dumb as you look.