When the priority of a Request(cr) is downgraded (e.g. from Priority 1 to Priority 2) the service type attached to the request does not change to the service type attached to the downgraded priority by default.
Component: Service Desk (all releases)
Install cr_allow_sla_downgrade option from Administration -> Options Manager.
Note: Requires Service Desk services to be restarted for the changes to take effect.