[citation][nom]Strider-Hiryu_79[/nom]What's "bannable" is any violation of the TOS(terms of service) and/or EULA(End-user License agreement). Harmless or not a violation is a violation.Familiarize yourself with those two abbreviations.[/citation]
Basically, its an exploit. Just because there it doesn't require special code in a client, does not mean you're in the clear. Item duping is an exploit, coin duping is an exploit.
In EQ2, when some people found out they could transmute items in battlegrounds, then come back and you would still have the transmuted item, lots of people did it, even though it was an exploit.
They shut it down and banned people who did it excessively, some they removed all the items they transmuted and gains from them. People whined. They cried. They said they were "only testing" it out. yeah, sure. They hear that its a bug and decide to test it out?
If the exploit was connected to some kind of currency outside of game, you'd bet you'd be in legal trouble for stealing or fraud, why is the same type of act supposedly ok if its just ones and zeros in a game?