Mountain Lion aggressively hibernates
ML 10.8.2, mid-2012 15" MBP (non-Retina).

This problem just popped up for me a couple weeks ago: leave MBP sleeping for X hours, unplug MBP, MBP lights/wakes up, enters hibernation.  Really annoying to open the lid only to have it shut down right in front of me.

My acwake was also disabled for both battery and AC.  Which means that the setting is now being ignored.

The solution appears to be (even though it's not referenced in the pmset man page):

sudo pmset -a autopoweroff 0

I should note that this does not affect acwake being ignored.  My computer still wakes up upon AC connect/disconnect, but it's not hibernating or attempting to hibernate after I've unplugged the computer and opened the lid.