Theres no fucking dupe bug.
They de-level to keep doing the Lard Orc/Shadow Seeker weapon quest. (kill 20/30 Shadow Seekers/Lard Orcs)
Why? Because you can get a Viper Staff +3/5 (mages) and sell it to the shop for over 300k.
And no, it's not a bug, it was intended for low levels, but some china people want to abuse it.