On the view profile page ( /secure/ViewProfile.jspa ) it's possible to update your user profile ( /secure/EditProfile!default.jspa?username=admin ) to an invalid email address. See attached screenshots.

This is problematic when users want to update their profile to reflect being out of office ( appending something like "out of office 9/29 - 10/2" to Full Name ) and inadvertently update their email address to their username by mistake which can happen often with password helpers and auto-fill