Archive.php returning fewer posts than expected

Hi everyone,

I’m running into a mysterious situation regarding the number of posts displayed on a year archive.

Specifically, for one year (2009), WordPress is returning fewer posts than expected. Judging by the count in the admin, it should be showing 12 posts for 2009 but is instead showing 3. I know the other ones are still published since I can access them directly by URL. This seems to affect only 2009 since other years work well.

If I “unpublish” the oldest of the 3 posts showing in the archive, the next oldest post appears. So, the Published flag isn’t to blame.

The main blog listing page doesn’t seem to be affected by this–it shows posts in 2009 which do not show up on the 2009 archive.

The posts don’t seem to have front-end XHTML issues, since the posts aren’t being rendered into the page at all.

Curiously, if I set the “Show at most” value to something greater than 10–say, 20–then they all appear as expected. Obviously, this is a hack.

So, I can only imagine the issue is related to what posts The Loop decides to show. I can’t find much useful documentation about whether The Loop has any limits (based on publish date or otherwise). Perhaps there’s some paging going on that I’m not aware of? My archives don’t implement pagination to speak of.

Any thoughts?