In the release editor (while adding a new release) I go to the Recordings tab. At first my tracks have no recordings associated so it says "(add a new recording)". Now for one of the tracks I click on the "Change" button and then on the magnifying glass to start the search. It comes up with a list of matches.
If I select one of those it will close the list. However if I just click on the "Done" button (because I decided to have it add a new recording after all) the popup on the right vanishes but the list of results doesn't.
I'm on Ubuntu/Gnome with FF 3.6.17.