We recently noticed (after publishing our eleventh podcast episode) that the first podcast episode has vanished from the feed. It isn't on the iTunes feed and it doesn't appear in the /feed/podcast/ rss document anymore, although all the other episodes are still there and appear to be fine. The mp3 file is in the same place and re-validates when I check it via the blog post in which it was originally imbedded and posted.
Basically, everything was fine, nothing changed, and now the episode is gone.