Comment 3 for bug 1180194

Ok, have submitted a patch
https://reviews.mahara.org/#/c/2242/

To test:

Before applying patch:
1) Set up a mahara site with an institution that has more than one remote authentication type
2) Add a bunch of users to this institution and give them a remote authentication choice (can all be same or a mix different types) and make sure each has a remote username - this can be checked by going to Users -> get report for the users in question.
3) on the Users page select the ones you want to change and click 'Edit' this will take you to the /admin/users/bulk.php page
4) Select a new authentication from the 'Change authentication method' and click 'Submit'
5) Check users again by going to Users -> get report for the users in question - it should now show that they have lost their remote username

Now apply the patch and do steps 3 - 5 above (or start with new users) and this time the remote username field should contain their remote username as expected for the auth method they are on.