Stock gets added instead of removed

[solteccc]

So about two weeks ago we had stock taking in our company. Now our accountant went to
Items -> Inventory Items -> Quantity Adjustment
to remove a stock item that was not in the workshop anymore.
However, another item gets added (without any further information like serial number of course, just a dummy item) instead of the wanted one removed. That happened more than five times until we gave up. Adding items works just normal.
Has anyone else experienced the same or even better has a solution/workaround to that?

We are using the newest version of weberp.