Are you saying that field 7 of root's /etc/passwd field is /usr/bin/ksh?
I doubt it as the system absolutely won't boot.
I'll bet that root's .profile is flipping root's shell to ksh *after* the boot's complete *when* root logs in.
Remember that /usr has not yet been mounted when root must run stuff at boot time, so the system does *not* run root's .profile. It simply relies on root's shell entry in the passwd file.
The other possibility is that there's *another* UID=0 account in the passwd file ahead of root and it has /sbin/sh for it's shell.
The system is not looking for username=root - it's looking for UID=0.
My $0.02,
Jeff
PERSEVERANCE -- Remember, whatever does not kill you only makes you stronger!