I must be missing something because I just couldn't figure out why some things went over my robot and some just fell through my robot(s). Also, I encountered the same stackoverflow as below very early on playing.
Thanks for the feedback. Trying to track down the bug.
So items must be carried over to their adjacent conveyor belt. If they are in the act of falling they will continue to fall through the robots.
Ah ok, will probably go back and play it again now that I know this. Hope you find that bug!
Indeed I did! Patched version is now available.