shutdown failure

Talkin' about late 2008 MacBook Air, OS 10.7.4, hooked up to a LED Cinema display, via usb-->ethernet adapter into the net, Logitech mouse MX1000 via usb stick, Apple BT keyboard.

Ever now and then - it may be related to the LED cinema save energy mode causing shutting down the internet connection etc. temporarily - my AIR refuses to shut down or restart.

Both ctrl-eject or clicking "restart" or "shutdown" under the Apple icon behave normally, BUT, the computer continues to be switched on and fully operable as if you never would have tried to switch it off.

Two "remedies" so far: Press & hold the mains button (kind of brutal) or turn on the command window and key in "sudo shutdown -h now".

Btw: IF the AIR refuses to restart/shut down AND there are directory windows open, these are opened after reboot even if I chose not to open them (as it is now the default with Lion).

Any hints are welcome.

SEV