Well I've been mining a lot for a few days and I finally decided to sell a bunch of the iron ingots I got. So I sold 9 stacks for 28.8k. And then I continued playing. Only to notice hours later when I typed /bal I had the same amount of money as I did before I sold the 9 stacks. I still had a bunch of iron ingots left over so I decided to see if it would happen again, and it did. Only this time I recorded it: I hope this gets fixed and that I get the money that disappeared on me.
My bal is still the same, and I'm not sure if the glitch still happens, I don't have enough iron to sell the 9 stacks.
It seems like it's not only the Iron. I just sold a stack of Diamonds and didn't get any money from it either.
It would be hard to pin-point the ones that are broken, as some of them work. I got money from selling a single iron ingot.