Poweroff doesn't power off

Hi, I experience sporadic malfunctions of /sbin/poweroff (launched by pressing the power button). It leaves a message like this on the screen: [8383.434840]: System halted and the computer remains powered on. It's not a big deal, but I wonder what could be the reason. I definitly haven't done anything special in these cases. Any ideas? Bernd -- http://sudrala.de