Jakov
Ellipse does not prevent aquittals that will result in negative balances. The reason is to allow the issue to be processed in the system because obviously there was a physical quantity that could be issued and it wouldn't make sense to not reflect in the system what has already happened in reality.
There is a report (MSR172) that you should run daily, which will tell you what items are into negative balances, so that they can be corrected.
You could also try to control it procedurally saying that the warehouse won't deliver items that would go into negative, but try telling that to a maintenance guy with a shovel down due to that item!