keyone will not stay in vibration mode

I have a CDMA keyone BBB100-3, running version 7.1.1. My problem is that when I place the phone in vibrate or silent mode it will, after random time, revert back to audible notifications. This is annoying in places where you want your phone to be silent. I put it into vibrate or silent by selecting it when I push the volume key up or down. I have also tried by depressing the volume key all the way down. When I did it just now within a minute the vibrate icon went off. Has anybody had this issue?

Why not slide notification tray down twice and then do not disturb mode set until you turn it back on again?

I found with my Priv, no matter what I did, I always seemed to accidentally bump a volume button at some point and my vibrate notifications became audible notifications. Because Android isn't BB10, there's no setting for "Volume keys control media volume only", so I downloaded an app (Rocker Locker) solely for the purpose of doing this, and remembered why I miss BB10's Notification Profiles so much.

Supposedly Rocker Locker is a bit of a battery drain, but the problem went away once I'd installed it.