I am clicking some time here on the site, managed to login into the bug report jira. We use jira at work so i am not uncommon to it. I would like to add a comment / submit a new bug.
User A has privileges to read Forum A.
If a new topic has been created, and this topic has been moved to Forum B, where A has no rights to read, and a link has been left in Forum A, the topic can be read by User A if he has not read the topic yet before it has been moved.
User a has just to click the "view new topics" and there its listed once.