I tried the following in Safari first, no cache cleaning, didn't quit Safari. I did log out of both sides first though.
I registered a new user at MacTech. After I clicked register it brought me to this, Log-in successful, but access denied;
It didn't show me as logged in under the User/Login menu on the main site, it still had the Login option.
Then I clicked on the Forums link from the main page, but instead of bringing me to the forums it brought me to the user agreement screen for the forums instead, so it actually did go through the process of logging me on but didn't show it at the main site. I agreed, it logged me in, but oddly my unread posts matched my Reboot account, it should have shown all posts unread. I had been logged in as Reboot before logging out.
It still didn't show me logged in at the main site though even though it had logged me into the forums. I then went back to the main site and I was able to successfully log in. I then logged out of both sides. I then logged in at the main site again and it logs me in to both that and the forums. So once the glitch of registering has passed it works as expected.
Logging in the second time, then going to the forum showed all posts unread like it should have.
I then tried all of the above in FireFox with another new user, except FF was clean, cleared all cookies and caches and restarted FF. It did the exact same thing as above, except for the unread post count thing, it showed all unread like it should have.
Edit - If I log in at the forums it doesn't automatically log me in at the main site like logging it at the main site automatically logs me into the forums. Will the forum log in link be gone eventually?
Edit #2 - I didn't try logging in to MacNews.