I clicked on a link back to a forum discussion in an email I received. I think it was this discussion. http://moodle.org/mod/forum/discuss.php?d=159359 possibly this one http://moodle.org/mod/forum/discuss.php?d=159516
That redirected me to the login page. After logging in I was sent to http://moodle.org/pluginfile.php/53/group/icon/200/f2 which I believe is an image URL. That page says "Sorry, the requested file could not be found"
From memory we store the requested URL in a session variable. After logging in the user is sent to that URL. Maybe the URL for the image request is overwriting the page URL in the session variable.