Some ways to break your syndication feed

To follow up my previous entry, here's the sort of thing I mean by the term 'broken feeds', as taken from things I've been frustrated by in the wild:

• advertise a feed on your site, but never update it.
• silently stop updating your feed because it's moved to another URL.
• put in partial entries that look like full entries.
• don't include all of the new entries from your site in your feed.
• include entries in your feed that aren't actually there on the site. Bonus points are awarded if they are partial entries or otherwise require content from your site that isn't there.
• stutter: have your feed repeatedly show the same entry as a new entry by doing things like changing the Atom <id> of blog entries.

Technically I should count things like removing your feed or having a feed that doesn't validate or has mangled formatting, but I don't really; those are relatively easy for me to see and deal with. The kind of stuff that I really consider broken is stuff that either causes silent information loss (the first four) or makes me do extra work for nothing (the latter two).

(I have actually seen feeds that had both missing entries and extra entries, with the net effect that I had to read both the feed and the site to get a full picture.)