kivy song.stop() sometimes doesn't work, on what does it depend?

I am writing a quiz app that has a song playing in the background, so I load the music and set it to play using song.play() . That works fine, but when I finish the quiz it shows the stats, and I want the music the stop, I use this code: song.stop(), and it works sometimes but not all the time! I don't understand from what does it depend. Maybe it's because I have another sound triggering after stopping the current song?