I don't know how I managed to make that happens.
I have "Current orders 4/3" in the bottom left button of my workshop window. When I click that button, it shows 3 crafting (3 Electrum Ingot) in progress (that is normal).
I check the delivery box and there are 5 items in progress. One is gathering and 4 crafting.
And the 4th order (Stilled Water) is producing as it is finishing stuff to the drop box.