Last page added becomes homepage

Something strange is happening with (at least) 2 of my WP 3.0.1 sites: the homepage URL gets redirected to the last page I added. So it becomes the landing page, and going to the homepage redirects to the URL of the past page -even if that page doesn’t exist anymore.

For example: I added an ‘experience’ page to my https://www.herkocoomans.nl site. I do not have any static page set as homepage, I just want it to show the blog posts (default setting). But somehow, now everyone gets redirected to the https://www.herkocoomans.nl/experience/ page, with a ‘sorry this page no longer exists’ message.

I checked the .htaccess, and that’s normal. So it doesn’t come from that.
I also checked the database values in the wp_options table. There’s no reference to the new homepage there, so its not a setting somewhere.
The site is set to display blog posts, the setting has been reset and reconfirmed.

One site that has this problem is a WP3 multi-site configuration. The other is just a regular single-site install.

Please, can you help me find out what could be causing this? I’m going to compare plugins next…