Multiple User Conflict in SharePoint: User changes after clicking ok in People Picker/Address book

This happened recently while I was trying to add a user on a SharePoint Site. User A was replaced with User B.


Problem

• While searching for a user in Address book by typing the name, say "User A", it shows the correct user. But once the user is added by clicking OK, it changes to say "User B". 

• When searching the user by domain\username (for User A), it only shows two occurrences of "User B".

• There is only a single letter difference between both of their usernames. E.g : For UserA- domain\samename1, For UserB-domain\samename

Solution:

• Check in   /_catalogs/users/simple.aspx. Delete both the users from it.

• Run both full and incremental import of user profiles in SSP.

• After this, try adding the user again.

Root Cause:

• The problem was in the user details. Old data was conflicting with new one. Once old data was deleted from  /_catalogs/users/simple.aspx , the user was correctly added.