Field Validation Not Working on Profile Form

Hello,

I have a form field for nickname, which I have it validate as Unique Username on the registration form. It works perfect during registration.

However, I give the option to change the nickname on the profile form, but still put in the validation of Unique Username so that they can’t change their nickname to one that already exists.

The problem is that the validation does not work when the user edits the profile and changes the nickname field. Can you advise what might be wrong?

Thank you,
Mari