Duped items are actually a simple fix for any decent programmer. Just run a script to change Item instance ID if it already exists. The problem is a lack of a decent programmer which resulted in the duped characters in the first place in addition to the many other errors made since Gravity LLC took over.
This!
The same would be for a server transfer... just change the server ID... or if the devs is not able... copy the char, but then delete from the original server.
But have you ever considered the problem was something that Gravity wanted? Try to imagine... duped items are good items (like hearts, armor,...) and at the time of the cloning, it wasn't so easy to get items + 30 without mall... so if you look at Gravity side: hey let's give players some good items for free, so then they will reinforce (and pay for them) and maybe they will play on both servers (so they will spend double money). Can we really consider it a mistake from devs? Or just a greedy action?