That's not really a bug
The system remembers the last address you have been to. In your case, this was just http://www.funtrivia.com/bb.cfm
because your last action before taking the quiz was to make a post in the thread.
That URL (as you already found out yourself) needs some parameters to work. When you post, these parameters come from the posting form. You later went back to it, but of course without submitting a form - you get an error.
This is an unavoidable issue - if the "Where I was" is a page that implied an action, you will always get an error. (That's of course still better than the alternative of inadvertently repeating the action!)