Certain kinds of files cannot be replaced or updated when you set Windows Disk Protection to temporarily keep user changes on a Windows XP-based or a Windows Vista-based computer (10 Dec-08)
Quote:
Symptoms:
You have a Windows XP-based or a Windows Vista-based computer that has Windows SteadyState installed. When you set Windows Disk Protection to temporarily keep user changes, certain kinds of files that the Windows boot loader accesses are not replaced or updated.
http://support.microsoft.com/kb/960838