Hello Salva,
we usually don't do backend changes.
here is another example.
It looks like inventory was taken out of the first inventory, as I have -15 there.
on my current inventory there are 13 left, although the stock is emtpy (it was about 28 - so it seems that it deducts from the already emtpy inventory)
the problem is, my shop shows still stock although there is none, and especially as we sell food, the lot numbers are probably incorrect.
I can see it also in the deducted stock of a current order, see screen shots attached. It used the inventory with lot number B28941.0 - which is old and empty and has no backorders enabled