Torsten has a blog post about an interesting bug in RSS Bandit. If you are subscribed to both Joe Gregorio and Ian Hixie's blogs then one of the entries in Ian Hixie's blog appears with the wrong date. The blog post that appears with the incorrect date is the post State of the WHAT from Ian Hixie's blog which is linked to from Joe Gregorio's post 3270 Redux. Instead of being dated 2004-06-29 as appears in Ian's RSS feed it is dated 2004-06-05 which is the same date as from Joe's post.

The problem arises from a workaround we came up with to deal with feeds that don't provide dates. Many users dislike feeds that don't have dates and prefer that we display some default date for such feeds. What we ended up doing was using the date the item was seen in the feed as the date for each item. In many cases this date isn't accurate. Sometimes the inaccuracy of this date is particularly glaring when a post from a feed with dates in it links to one with no dates in the feed because it may look like a feed is linking to a post in the future. For example, Joe Gregorio's post dated 2004-06-05 links to a post made by Ian Hixie on 2004-06-29. In this case, this is valid because Joe Gregorio went back and edited his blog post but didn't update the date in his feed. However RSS Bandit thinks this discrepancy in the dates is because we guessed the date for the entry in Ian's blog and thus corrects it by aligning it with the date from Joe's entry. The rationale for this behavior is that guessing that an undated entry was posted on the same day as someone linked to it is more accurate than guessing that it was posted when it was fetched. The bug is that when we use this heuristic we don't check to see if the entry whose date is being adjusted is actually an undated entry.

This has been fixed in the current codebase. The next question is whether we should actually be adjusting dates in this manner in any case.