furnace connected to pipes is takeing metal ore and converting it to sulfur when sulfer is placed in furnace first

i connected a large furnace to 3 boxes (1 to output cooked items 1 to input ores from and 1 to input wood from) the ore box i put both sulfur and metal ore into and noticed that when the sulfur ran out it kept filling from the metal ore and was converting it to sulfur, i then tried reverse the process and it did the same was converting sulfur to metal to refill the furnace. it does not seam to do it every time but it seams to bug and do it about 1 out of 3 times i tried to repeat this( and once it bugs and does it it keeps doing it for as long as there is ore to refill the furnace with), so it is repeatable  just had to futz with it a few times to make it do it.  I did report it to help on discord and dragonzz came to see what it was doing and was sent to here to make a bug report on it  ( the bug can also happen even if there is both ore types in the box , it seams to convert to whatever type of ore that is being cooked in the furnace when it does happen). if need more info or clearer idea of how it was working just let me know ill do all i can to show/help on this as i know it is hard to sometimes get idea of what is going on thru a simple report like this