what the @#$! is wrong with post filtering?

I’ve partially figured out what is happening here. Posts aren’t actually improperly disappearing. Instead, they are being spit out in an apparently random order, instead of descending by date as they should be. When I scrolled back through all the older entries on the blog’s home page, the posts appeared to be all there but completely in the wrong order, both on the main blog and the feed.

I can’t find a bug there, so I think that you must be doing something else that’s mucking it up. I have no idea what it could be though.

Have you tried looking at the actual SQL query being generated?

In your wp-config.php file, add this line of code to the top:
define('SAVEQUERIES', true);

Then, in you can do this to dump all the queries and how long they took:

if (SAVEQUERIES) {
global $wpdb;
echo '<!--\n';
print_r($wpdb->queries);
echo '\n--!>';
}

Find the query that’s being generated by your code and see what the heck is wrong with it.

It just hit me: GROUP BY. That’s probably your problem.

If your posts are appearing in REVERSE ORDER (oldest first), then that’s definitely it.

Your version of MySQL has a bug:
https://www.ads-software.com/support/topic/154622

I find that when I comment out my code, I can affect the display of posts using query_posts() in my theme’s index.php, for example to reverse the sort order and such. If any of my various functions I’ve tried to exclude the category with are enabled, I cannot affect the display of posts with query_posts().

I’ll try your suggestion and see what I get.

Oy vey. We are indeed running 5.0.51a-log.

They’re not appearing exactly in reverse order. It’s -almost- reverse order, generally ascending, but there are some that are randomly sprinkled around.

Note that the current trunk may not exhibit the same issue, as a whole bunch more “GROUP BY” bits were removed yesterday (they were unnecessary due to other changes). The MySQL bug in question is specific to group by queries.

We’re going to rebuild our stack with MySQL 5.0.67 and see if that helps.

Upgrading to MySQL 5.0.67 solved this issue for us. It is a bug in MySQL, not WordPress.

See the trac ticket above and the link Otto42 posted for details. Thanks Otto for all your help.