when playing path wind , press the volume down to silience, but after playing a while ,we can still hear the sound

[quandan]

current build number: 47
device name: arale
channel: ubuntu-touch/rc-proposed/meizu.en
last update: 2015-07-06 05:43:41
version version: 47
version ubuntu: 20150706
version device: 20150701-cdd791c
version custom: 20150602-731-5-32

Steps：
  1.open the path wind app
  2.play the game , turn off the music by pressing down the volume key to zero
  3.continue playing the game

Expectation:

  as long as i play this game without quiting, there shouldn't be any sound

Actual result:

  After playing this game a while , the sound appears again automaticly