Reproduction steps:

• Create a fresh wiki
• Login with Admin and setup the right to prevent unregistered users to view it and to allow guest user to use it
• Log out
• Click on the top right area to open the drawer and click on register
• Fill the form and put 2 different passwords
• Click on Register button

Expected result:

• Ideally the click on Register should not send the form and the javascript validation should show immediately that the two passwords are not identical
• Even if javascript validation does not work, once the form is submitted the user should see that the registration did not work because of the 2 passwords not identical

Obtained result:

• The user is immediately redirected to the login form, there's no indication whether the registration worked or not