Comment 1 for bug 1180194

I was unable to replicate.

I set up a test institution with a few different external auth methods
I added a dozen users to the institution - all of which had a remote user name set.

I tried changing the auth method for some of them via the bulk update page and watched the authinstance and remoteusername db columns

I tried changing a bunch of users:
- of the same external auth method to another external auth method
- of different external auth methods to another external auth method
- to Institution:internal auth then back to an external option
- to mahara:internal auth then back to an institution's external option

The users changed auth method as expected but in none of my tests did the remote user name disappear