CRM-12869 This is a temporary fix from Eileen which prevents the over-writing of email address

However it also prevents the billing address from being saved for the payee, and requires the user to know that they need to manually replace the default billing field values (which are prefilled with data for the person being given the membership) with the payer's data (name and address). In general I do not think this "Record payment from a different contact' feature is production-ready (even though it is part of 4.3). Selecting a different payer should reload the billing name address fields with the payer info in order for this be usable IMO.