It's one of those things that never seemed to be figured out. Many people thought they just changed their mind on what color the bars should be but I suspect the trap was a prototype and they decided to use it. I know there were other things different about it but I can't remember what.
ah, here's an old post with some guessing:
viewtopic.php?f=3&t=8523&p=80290&hilit= ... ars#p80290