In this game, look at the furniteure factory at catserbridge.
http://list.extended.simutrans.org/~vladki/debug-saves/demo-14.sve
it requires steel, wood and textiles. It has no textiles in input storage, not even a contract with textile factory, but still produces furniture
EDIT: so this is not a bug, but a result of the save being too old. In the previous (standard) version the factory needed only planks, and filled its output buffer. When I connected it to furniture shot it started to deliver, until it ran out of stock. Now it is not producing any more.
Splendid, thank you for clarifying this. That is most helpful.