Contributed By: Don Cottam [MS]
The Automatic Updates UI probably isn't hanging, but is waiting for the service pack install to complete. There is no animation to indicate that the install is still continuing though, and you don't receive feedback about the install completing until it is done, especially since the install of service packs is done in quiet mode with no UI from the service pack installer.

The service pack install can take several minutes, especially on slower hardware, so the best option is to wait until the Automatic Updates UI indicates that the install was finished.