This seems to be the exact same problem as this was three years ago: Network manager doesn't remember login (username)
But I'm as up to date as I know how to get and I have the same thing. The password is remembered but I have to re-type the user name each time. It's really just kind of silly, but it is an annoyance to have to do this four or five times a day when the vpn falls over.
Any ideas how to fix this?