I just checked in a new version of SimplePie that uses md5() instead of sha1() internally to generate cached filenames. If you were using favicons and update to the latest version, they will probably all not show up. They will reappear in about a week’s time if you do nothing, and if you want to force them to reappear when you next update, run this query:

update fof_feed set feed_image_cache_date = 0

Usually FoF only re-checks the cached favicons once a week. This makes it think that the last time it checked was January 1st, 1970.