Logging in on pages not the main page will often result in a redirection that never takes you back to the page you were looking at.

Say I follow the link to My Account and I'm not logged in, it prompts me to do so, I do, it redirects to the main page and not my account page.

If I try to reply to a forum thread though I am not logged in, it prompts for the login, I do so, it redirects to some non-existent part of the forum and I have to click back to get to where I wanted to be.

Say I'm viewing a thread and I realize I want to reply to it, I am not logged in, I figure that clicking on Reply will take me to the dead page and waste my time. So I use the login form that sits just below the Search and Browse links. After login I still get a forum page with no content on it and I have to back back.

I've had this same problem, only with changing my sig on the forums. Seems to like to redirect me to the main page. I get logged out on occasions, but I seldom get re-directed.