I'm not sure. That's not an issue we've heard of in a long time. We used to always update the user's email to the one of their social network, but that functionality was removed well over a year ago.
Can you do a few tests to see what circumstances this happens under, that would really help us narrow things down:
* If you disable the Social Profiles - CB plugin, does the email still revert on the next login?
* If it works properly while disabled, can you re-enable it, but set the "Always Import Profile" setting to "No" to see if that fixes it?
* Also, what version of CB are you using?
We'll help you get to the bottom of the problem.
Thanks,
Alex