I have to agree with Howie. MySQL is clearly to blame for this, but they have not yet released a GA version that fixes the problem, so you can't really blame our hosting providers for not wanting to upgrade.
In my case, upgrading WordPress is very painful since I'm on 2.0.2 and there is no easy upgrade script to get me to 2.5. And even so, apparently 2.5 still runs into the MySQL problem.
It seems to me that the MySQL bug only occurs when doing a GROUP BY on just the primary key. As pointed out here:
"This can be worked around by simply removing the GROUP BY clause. Using GROUP BY on a unique index (a Primary Key, of course, is a unique index) is pointless as each row will by definition be its own group."
I am working on a patch for this issue but I could use some help.
If anyone is interested please shoot me an email (mpelzsherman at yahoo.com).