Duplicate registration page is displayed when creating a new user on Edge

STEPS TO REPRODUCE:

1. Login as Admin
2. Go to Administer Wiki > User & Rights > Users
3. Click 'Add user'
4. Fill in the username and password for a new user (e.g. U1)
5. Click 'Save'

EXPECTED RESULTS

The new user is created and the page returns to 'Global Administration: Users' where can be seen the list of all users.

ACTUAL RESULTS

When clicking 'Save', a new registration page with blank fields is displayed, identical with the initial 'Registration' lightbox (screenshot attached). However, the new user is created.

The issue reproduces only on Edge browser.