Bizarre behaviour with sudo

[Todd C. Miller]

I really don't know why that would be.  Sudo doesn't do anything
weird wrt password reading, it just uses the standard getpw*
routines.  Do you by any chance have a shadow password file lurking
around with your old password in it?  Sudo will use the password
in the shadow file in preference to a non-shadow password.  If
you want sudo to do password access the same way most redhat do,
you should configure sudo with the --with-pam option.

 - todd