Another account with same uid as root gets prompted to set new password for root, not itself

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http://unix.stackexchange.com – After upgrading the os from 5300-06 to 5300-11, this weird behaviour happened. My system had another unix account, let's call it "abc", purposely configured its uid to 0 for working as a root with all its authorities. It has been run like this for years and worked completely fine. However after the upgrade, when abc's password expires, rather than prompting immediately after its successful login for a new password, it is now asking to change "root"'s password, and it really is changing root's password not abc's. If I change abc's uid to another unique id, it will successfully says to change (HowTos)