Wake from sleep when I plug AC power

Hi all, lately I've been noticing that my Macbook Pro wakes from sleep whenever I plug in the AC adapter.
I've looked in System Profiler/Power/Battery Power and it says: Wake on AC Change: No.
I have a feeling this started happening after a software update, anyone else experiencing this? Could it mean that my power adapter is delivering more power to the computer?
Thanks in advance.