Let's just keep in mind that everything North Korea is doing now is designed to keep Jong-Il in power. It is all for the Kim family mafia/dictatorship.
They don't really care what China wants or doesn't want. All that matters is keeping the Kim family in power. Sometimes that matches up with what China wants and Chinese interests. Sometimes it doesn't.
Bingo. All this talk of being a Chinese puppet is just that. Talk. The domestic and foriegn policies of the North Korean regime have one goal; to keep Kim Jong Il and company in power. North Korea has friends and foes only insofar as they relate to that goal.