Using in Firefox browser on iPad and playing with four fingers. When I go to move all four fingers to change the pitch of all four notes this causes my iPad to attempt switch to a different app. When I then release all four fingers the notes I was playing 'stick' and continue to play. To stop them I have to refresh the page.
The point was more that the notes 'stick' after I return to the Firefox window. With four fingers playing the sounds can be a little wild. It took me a couple of tries to figure out why it had happened so I am guessing another user might be similarly confused.
Not to take anything away from this delightful little app. I just wanted to help out by reporting a little bug I found.