I was supposed to leave for holidays on August 1st, but a summer fever held me back.
As it became traditional, I took the chance to do some Gnash hacking, approaching a bug that made playing Super Mario Bros unpleasant. The mario sound didn’t stop on game over thus overlapping with the new sound started for the new game. Annoying.
After some research the help came from Jan Flanders, an usual attender of the #gnash IRC channel. He pointed out that calling .stop() against an unattached Sound object should stop all playing event sounds. It took a couple of days from there to an automated testcase and a fix.
You can now Enjoy Your Mushrooms !