So, basically this is how the duplication glitch works:

1. Vanish
2. Spam click a chest so that multiple instances try to open
3. Simply take the item out of the chest and place in your inventory (It won't try to take it off your cursor like it should)
4. Relogging/reloading the chunks will show the item still in the chest, but also in your inventory.

This is kind of a huge issue that needs to be fixed, I found one of my moderators getting HUGE amounts of items. The thing is, this trick is so easy that I'm surprised it's not been noticed. Be careful on who you give SilentChest to until you have a fixed version server owners...

I'll leave this public because anyone granted vanish access is presumably a trusted staff member.

Trying out a fix now. Have you been able to do the duplication yourself, or just heard from your moderator?

You can try the build at http://ci.kitteh.org

I've tried it myself, and the moderator in question was promptly demoted and banned. Although, I do give out a few vanish options to my VIPs, but only simple vanish. (Not silentchest) so it doesn't always have to be staff.
Thanks for the fast fix, I'll put it on now.

Had the new plugin running for 3 hours, asked multiple moderators to test it and it's all fixed and (seems to be) stable. Thanks!

Will be in the 3.18 release :)