Jelly Bean :: Quiet Mode Randomly Turns On And Blocks Calls - LG Optimus F3 4G LTE

I'm on Virgin Mobile, LB Optimus F3 4G LTE (it wasn't an option in the forums, so I came here instead). Not sure if this is an Android feature or an LG feature.

Anyway, this thing called "Quiet Mode" will randomly turn itself on at nighttime or in the middle of the day with no warning and silence all sounds and block calls from all contacts. This is obviously frustrating. I'm not bumping it in my pocket or anything -- you can't even turn this mode on without unlocking the screen and scrolling all the way over in my top pull-down bar. For instance, it's been sitting on the chair next to me for the last two hours and I just checked it and it's been in Quiet Mode for who knows how long.

I can add contacts to the allowed calls list, but I still won't hear the ring, and I can only add a limited number of contacts. Also, all the writing within this mode is really poor English, which is odd. Example: "Please mind that incoming calls with exactly the same numbers with below list will only be allowed." Anyway, it can be scheduled for certain times and I'm going to try scheduling it for just one minute from 4:00 - 4:01 AM every night and see if that satiate its compulsion to be in control.

Any ways I can keep it from doing this otherwise? It doesn't appear to be an app that I can fiddle with.