If two people are looking in the same station's GUI while one crafts an item, the crafted item remains in the output slot for the second person unless they close the GUI. The main issue with it is that it's incredibly easy to duplicate the crafted item since when one person crafts something then it doesn't properly register for any other players in the GUI

Seems like the syncing for the inventory in general is very whacky in multiplayer. Two players trying to use a bench at once causes quite a few issues, including deleting items