If booted to a system folder on a RAM disk, and you attempt to Shut Down, you get an error dialog with a message that there is a problem trying to write the Persistent RAM file, and data will be lost if you shut down. You are given a choice to either Shut Down, or Cancel.
The behavior has been traced to Assistant Toolbox 1.2, the extension file that manages the Persistent RAM disk. It has also been reported on the PowerBook 520 and PowerBook 540 models.
A workaround is to revert back to Assistant Toolbox 1.1 (the pre-System 7.5 version).