Ez feauture :D
https://forums.oneplus.net/threads/guide-bugs-fixes-and-how-to-use-new-… <- Itt a 4. post írja is, csak veled biztos nem beszéltek;)
"Volume not lowering to 0 or not able to put the phone in vibration- I talked with lots of OnePlus 3 users and used Oneplus 3 myself this is not a bug it was intentionally done by OnePlus Developer Team. And you can put your phone to vibration by following the guide in #1 post"