11z turns itself on after a proper switch off

I have this 11z laptop less than a month, light usage. Now I got a problem with it.

I have found several times 11z turns itself on after I switch it off from windows 7.

This 11z turns on itself  "without" I press the power button after I switch it off from windows 7:

1. Try to unplug the battery (just unlock the battery but it is still attaching), it turns on.

2. Plug the battery in, it turns on.

3. Close the lid, it turns on.

4. Plug in the AC power, it turns on again!!!

Right now, I have to unplug the battery to make sure my laptop is switched off.

I have sent an email to the Dell tech support and waiting for their reply.

Any people have an idea what happen with this wired situation?