It's not a quirk. It may just be a setting not how you want it. If you are using a terminal at the serial port as your console, it can drop to the [tt]ok>[/tt] prompt with a certain keystroke. Doing a Stop-A or a BREAK on a serial keyboard will drop to the [tt]ok>[/tt] prompt. What might be happening is that your terminal on the serial port is sending a BREAK when you are powering it down.
You can disable this action by going into [tt]/etc/default/kbd[/tt] and putting in a line that says...
[tt]
KEYBOARD_ABORT=disable
[/tt]
This should turn of keyboard abort. See [tt]man kbd[/tt] for more info.
Also, some Sun servers have a key switch with a Secure position. Putting the key there will keep it from dropping to the [tt]ok>[/tt] prompt when a keyboard abort sequence is hit.
Hope this helps.