This happened in XS too...
Usually I use notifies. If I receive a mail who notifies an answer to a private forum (like VIP Area or something like that) and I click on the email to the direct link to the post, if I am not logged obviously the forum asks me to log in.
After the login, instead of redirecting me automatically to the requested post or to the forum index (like default when login/logout ) it shows
"The topic you requested does not exist"
(but of course the post exists, if you reach it by forum > topic > post )
I think it could be considered as bug... is it possible to redirect automatically to the requested post or at least to the forum index?