1) If VC is executing commands even when you are sure that you are in standby mode, then you need to change your prefix, or increase the required prefix confidence.
2) If you want VC to return to standby automatically you can set this in Options. Look at the attached image:
It is very difficult to use VC with only voice when you are watching movies, listening to music etc. It is more reliable to at least use a remote control button to turn VC on and off. With the amulet remote this is done automatically when we lift the remote (on) and put the remote back down (off).