Disabling a payment processor via UI (other than Payment_PayPalImpl) will break live mode

Confirmed both on client site and local dev instance.

Steps to reproduce:

• Configure a payment processor (any which is NOT Payment_PayPalImpl)
• Inspect values in the civicrm_payment_processor table, confirm that the "live" instance is NOT class_name=Payment_PayPalImpl
• At civicrm/admin/paymentProcessor?reset=1 click "Disable"
• Click through confirm screen
• Inspect values again in civicrm_payment_processor; live processor will have had its class_name change to Payment_PayPalImpl rather than the correct class for that processor
• Re-enabling the processor will leave the live version now in a broken state

Other values in that DB table seem to be similarly affected (eg billing_mode will be set to 4).