Why do some of my apps not play the sound notification when I leave the app open? Textra does not seem to play the sound if it is open. Also T-Mobiles Digits does not always play the sound either as well as some mail apps. Is there some setting someplace I need to check beside the do not disturb setting? I believe I have that off. I'm a new windows phone convert so I'm not 100% sure of this OS yet.