Is this a bug, or perhaps i'm not doing something right. But here's what I did:
I logged in to a test blog I made, ie http://test.blog.com, but I logged in from the main site, ie http://blog.com. It redirects me to test.blog.com fine, but the logout button on test.blog.com doesn't work, unless I run the link from blog.com without the 'test' in front of it.
I assume it's setting the cookie on the parent, then redirecting to the subdomain, hence why it can't clear the cookie when you try and log out of the subdomain..
Lost yet?