I have FW 2.1.4 and sometimes the same problem, it wont turn off.
I have noticed this happens when i end a movieview and i press return often fast to get to entry level to power off.
When i go out of the movie with return and wait 8 sec to next touch to return i get a good close.
Iam not a programer, but i think the prob is when you get too fast out, the sistem get hang closing apps, closing netconnection and the the poweroff commando dont work. Its my experience. THX