Should be fairly simple to track.
Earlier today, I checked in, noted that my diamonds had sold well.
/find diamond -> "There are no diamond for sale."
Cool. Get some diamond blocks for $500/diamond or so. 37 of them.
Sell 256 diamonds for $550 (I think) each.
"You now have 320 for sale at blah blah.." what? There were no diamonds for sale.
Later today. Checked vshop. 2 for sale @400, seems to be working again, but...
I have no diamonds for sale, none were purchased. They disappeared.
I can provide further details if needed, but that's about how it went. Would like 256 diamonds back, since that's all I can reasonably expect you to have tracked for today.
EDIT: Whee, happened again, right after I typed this up. Sequence:
(had 77 diamonds in inventory, none on shop -- you should definitely be able to see that sale command.)