Normally, pressing the power button once initiates a shut-down in Windows 7.

If any programs are still running that will not quit (e.g. waiting for a dialogue response), Windows overlays the screen with a dialogue allowing the user to cancel the shut-down.

I've just noticed that on two different systems here, using this cancel option disables the shut-down via power button. The power button can still be used to kill the system by holding it for a few seconds, using the Start menu button to shut the PC down still works as well.

Steps to reproduce:

1. Open Notepad, type a few characters. Do not save.
2. Press the computer's power button.
3. Wait until the dark screen appears.
4. Press cancel.
5. Press the power button again. Notice how nothing happens.

What is the reason for this behaviour, and can it be disabled to always try and shut down the PC when the power button is pressed?