This is a product defect 85601.
Steps to reproduce:
1. Select a user, go and change his password using Manage My Passwords workflow
2. After password change select Manage My Passwords workflow again and enter initial password (that was changed on step 3) in current password field.
3. Observed: PM Accepts the initial password, but on the next step if cannot change it
4. Expected: PM must not accept the changed password