The URL format of Stack Overflow is of the form .../id/question-title
If I add some more text at the end of the url like .../id/question-title-pink-unicorn and hit enter, the page is refreshed and the url is stripped of the pink unicorn I have just added. So far so good.
Then I change the url to .../id/question-title/persistent-pink-unicorn and hit enter, the page is refreshed and my pink unicorn is now a part of the url.
Edit: This doesn't look like a question so here is the question: Will you allow my pink unicorn to reside on the site urls or this is something that should be fixed?