http://www.flyertalk.com/forum/showthread.php?t=362998

This disappearance was guaranteed earlier and was one way of finding out that they did wait list you.

There were some reports that it was fixed and for one of my itineraries reported in the above thread, the itineraries stayed visible until one leg cleared and then it disappeared. I made another transatlantic booking and that disappeared as soon as I was waitlisted on both legs.