When you do a search and go to a thread. hilit is included in the URL which highlights keywords in that thread. But with phpBB 3.0.12, if you clicked the larger thread title text link (check image showing arrow pointing to that link), hilit would be removed from the URL when clicked, but using friendly URL's in phpBB 3.1 does not remove it from the URL when you click the bigger thread title link after first landing on that thread doing a search with keywords highlighted.

I'm using friendly urls with phpBb 3.1 Beta 2