Win XP Turn-off has option to install updates on shutdown - how do I get rid of it?

After installing the Win XP SP3 update successfully on my Dell Dimension 4700 and setting the "Notify me but don't automatically download updates" option for Automatic Updates, the Turn Off button in the Turn Off Computer dialog box has a shield symbol representing the option to "install important updates" prior to shutdown.  Although there is an additional option to "Click here to turn off without installing updates", I want to go back to the "clean" buttons I had originally.

Why did the Turn Off Computer dialog box change after the SP3 update?  The same update was performed on a Toshiba laptop and the Turn Off Computer dialog box didn't change.  The same Automatic Updates option was set for the laptop as it was for the Dell 4700.

Can anyone solve this mystery?