Currently if you create a new user with the account page and modify the details you end up in an inconsistent state.

Reproduce:

1) Go to create account details page and fill in
2) Press Next
3) Press Back
4) Change account details
5) Press Next

The modified details are not taken changed as you've already created user account and the page is set to completed.

I see three options to fix this..

1) Set the page to insensitive after the account has been created
2) Make sure the user account is only created at the end of the setup
3) Support changing the account by deleting the created one and creating a new one if when pressing next the values have changed.