After seeing a lot of noise on possible item duplication, I did some thorough investigating. It turns out, yes, some players were using an exploit to duplicate items.
I don't need to explain why this is a serious problem, so I'm just going to describe what I'm doing about it.
1. I removed duplicated inventory from offending players. They will not be banned right now because this was not technically "hacking". HOWEVER, now that this is a known issue, any player caught attempting it in the future will be BANNED.
2. Any players who discuss techniques for duplicating / patching / hacking / etc. will be WARNED and then BANNED if they keep it up.
3. I've added new protections to prevent this from happening again, and I've added some watching scripts to automatically notify me if anything looks fishy.
It's extremely dispiriting when I have to spend my Deepworld development time dealing with cheaters and problems instead of making new things. If you ever know of an exploit, please share it with me AS SOON AS POSSIBLE so we don't have to waste our time with this again, and I can focus on fun new things for everyone to enjoy.