Well, I don't know what to tell you - I just tested both of those scenarios and they both worked as expected:
1. Used the volume down rocker on the side to put the phone in vibrate mode
- watched the screen for 3 minutes (amazing, Smart Stay actually worked like it's supposed to!) and the phone stayed in vibrate mode
- stopped watching the screen and let it time out by itself, waited 3 minutes, pressed the power button on the side to wake it up, and it was still in vibrate mode
2. Repeated the above, except this time using the volume rocker to put the phone in silent mode - same results.
I'm running 4.1.1/Verizon in case that makes any difference.
It sounds to me like you both either have 4.1.2, or you've both installed some app that's causing this behavior. I'd suggest that one of you perform a Factory Reset and see if it corrects the problem - if it does, then the other person needs to do the same.
Without playing 20 questions to see if we can narrow down what app or settings might be causing this, the Factory Reset is the most straightforward way to get to the bottom of it.
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