Is Power Button under software control?

[clare]

Hi,
I have had no end of trouble trying to get the Power Button to make the 
tiny click that shows it has accepted my press. (With Aux pressed).

Lately I have assumed that because the shutdown process is s bit
flaky, if it is not really off, the Power button may for that reason be
unresponsive to attempts to bring up the boot screen.
If I always take out the battery after shutdown, I no longer have a 
problem getting the power button to respond and start the boot.

Did I imagine all this?
thanks
clare