I still get this problem. Just ignores me when I say "Xbox On" all other commands are good. Anyone had any luck with why?
I don't know where the problem lies, but I would at least make MS support aware that you are still having this issue. My guess is that its a software issue, something related to what happens to the Kinect mic while the system is in standby.
I'm not sure if it would help, but there is a new 'Voice Studio' app that MS put out that has you speak several phrases while loud audio is being played. They are using it to improve the service, so you could try that out.