Actually, I've noticed conveyor belts sometimes have a sinusoidal motion... i have pieces that are supposed to go from conveyor belt to conveyor belt (often with a falling motion). Some of them will hit a conveyor belt and then start reversing directions.
I'm starting to think I need to look at rolling my own solution or do a lot more digging into the code and see if I can find out what is amiss.
I see, mayo, that you've had this problem all along... If you have any hack solutions that come to mind let me know.viewtopic.php?f=3&t=5413&p=25281&hilit=conveyor#p25281
I think the solution we're going to go with, because we're n00bs and can't think of anything smarter at the current time is as follows:
we have to conveyor belts. One doesn't collide with "blacklisted objects". It has a conveyor belt speed of -3 (left). The other ONLY allows blacklisted objects to collide and has a speed of 3. This allows both sets of objects to go the correct direction (at least the one we want it to be)