I tried to auction multiple stacks of something and it didn't sell. I then did /sell hand and I got paid for less than a stack, and all the other stacks had left my inventory. auction multiple stacks of thing no-one interested, thing returns to inventory (I presume) /sell hand you sold < 1 stack of thing, here is not much money check inventory and no things there I don't know if this is a bug with auction, or with sell hand, as I didn't think to check my inventory after the auction had finished.
@JamieSinn please look into this. If you find the issue, please get a ticket in github so we can track all this properly and work at it one by one.
Okay played with it a bit more. It looks like it's auction that's not returning the correct number of items. Auctioned 376 wheat Got returned 64 +56 Auction kept 256 wheat
https://www.spigotmc.org/threads/auctions-problem.135131/ looks like same bug, although its more complicated than that.
Negative stacks disappear when opening a chest, scrolling over them while they are in your hotbar, dropping them, grabbing them, trying to split then, ...
So... Auction 127 of an item: works fine. Auction 128 of an item: -128 stack Auction 129 of an item: -127 stack Auction 192 of an item: -64 stack Auction 256 of an item: 0 stack Auction 256 of an item: 1 item.