I have a site we wanted the login username to be the user's e-mail address. The user_login column contains the e-mail address. No problem. I created a custom function so that when the user updates their e-mail address on their profile page, the user_login column is also updated. Works like a charm.
The problem is, when you change the user_login value, the WordPress session gets terminated. Assuming this is a cookie issue.
Is there any way to stop the user from getting kicked out?