In the mystic forge if you put an item in to be forged but then move it back out over another item available to be forged it overrides that item. In other words if I have 10 mystic coins and I put them in to be forged but then took them out and dragged them over my ravaging shield, the ravaging shield icon gets replaced with 10 mystic coins, thus showing two stacks of 10 mystic coins. Now you cannot put both stacks in the forge, they still act as one item and you don’t get 20 mystic coins when you close the forge either, however you then cannot put the shield in unless you exit the forge and open it up again.
So, at the moment it is only a minor inconvenience, but I worry someone may find a way to exploit this bug.
Flickr
[img]http://farm9.staticflickr.com/8304/7960903816_5fa27da1d0.jpg[/img], on Flickr
-Deus Fatorum