I think what's happening is that when you select a song, that starts a countdown timer for when the "next song" action is triggered, but if you then select a different song manually before the duration runs out, that timer is still running. I can fix that in the next version. Meanwhile, you should be fine in a performance, if you let each song run for its full duration. If you need a workaround, closing and reopening the Perform window should reset any running timer.