The Japanese government demands phone manufacturers to embed within their phones an always-on shutter sound. That's because there are creepy weirdos that use their cameras on their phone to take upskirt photos on the subway and what not. Hence - the shutter sound is always on. Doesn't matter if the silence switch is flicked, if headphones are connected, it's irrelevant...
Before 10.1, you could set up Assistive Touch to be a Mute button, that once pressed really did mute the shutter sound, but now no more. I'm dying to find a legit hack for this.
How bizarre. Thanks didn't know.