Tmobile Visual Voicemail mutes ringer once message finishes playing in the app - only when phone is on do not disturb

ACTUALIZACIÓN:

I have it working properly by switching apps.

I uninstalled the Tmobile visual voicemail app.

I then installed the Visual Voice Mail by MetroPCS app (since it's under Tmobile).                         Version: 6.3738.93818

I no longer have the issue using MetroPCS app.

Hopefully Tmobile engineers will look at this thread and find out why their app is doing this. Just please don't mess with the MetroPCS voicemail app.