Reference Numbers in Service Request Subject (Redwood)

In the SUI for Service Requests, the Reference Number was automatically inserted the Subject Line for all messages (Replies and Forwards). In Service Center, the Reference Number only appears to be added to the Subject Line when using the Compose Email Smart Action. If the agent replies to the originating message, the Reference Number is not appended to the Subject Line automatically. Has anyone had success automatically adding the Reference Number when replying?