We have inventoria and express invoice. We experience issues with the stock quantity that keeps on changing by itself. Without any transaction involving the so said item.lets say i entered 96 of 1 product today, tomorow it could be -347 of the same item without selling any.
Then we also have trouble doing our invoice with express invoice since the item quantity is obviously unavailable for sale since -347 on stock. Also in express invoice we keep on having to redo all the time invoice that we enter because they magically disappear when we click save with payment.... i dont know but those two product of yours seems to have quite a lot of issues and relation link to fix