Editing a user's info, the email address automatically changes to your own email address. You have to manually edit the email field and re-enter the user's real email address. (could happen to the federation ID field as well)
This is a browser setting called Auto-Fill.
Disabling auto-fill will resolve the problem.
For example in the browser Safari go to > Preferences > AutoFill tab -- uncheck User Names and Passwords.
The downside to this is, if you want Safari to remember and fill out your Workfront Login username and password, it will no longer do this.