Ha, I found this topic that's nearly two years old now, because I'm encountering the same problem.
This is MAS 2.1. The login name is grayed out, showing the last+first initial of what was originally configured for the user. Changing the display name (First Name and Last Name) doesn't change it.
We use IE 11, because that recognizes the old-timey SSL certificates and doesn't give us warning pages to click through. But, I tried Chrome, and it's still grayed out.
Hopefully some fresh eyes on this thread can help us solve this.