Sprout, that thread is showing 4 Youtube clips posted by you at around the time you posted your reply above. They do seem to work correctly.
Because of there being lots of clips on pages on that thread there is a time gap between going on that page and the clips appearing. Initially there is just a white space, then the clip appears. The slower the broadband connection, the longer it takes for the clips to appear. It's possible your connection was slower than normal which made it look as if the clips had vanished.