Wizard detecting memberUid and other attributes doesn't save it

Steps

1. Use the zombie army from https://github.com/owncloud/administration/tree/master/ldap-testing
2. Create users and groups with the PHP scripts
3. Edit "Box10" and add a few zombies as members using the "memberUid" attribute.
4. Setup LDAP in OC
5. On the main page, click "Next"
6. Then click "verify"
7. Then "Next" twice
8. In the groups page, pick "posixGroup", then click "Verify"
9. Then go to the Advanced page and open "Directory settings"
10. See that "memberUid" is auto-detected and set
11. Refresh the page
12. Go to the Advanced page and open "Directory settings"

Expected result

"memberUid" setting sticks

Actual result

The setting reset itself back to "uniqueMember".

Versions

Seen on stable9.1 and master

@jvillafanez maybe some ajax race condition that doesn't save that setting properly after auto-detecting ?