Customize WSUS port to a value other than 80 and 8530

I've set up WSUS on Windows Server 2012 R2. I changed the http port to 8728. Then I find the following error in the event log:

The WSUS content directory is not accessible.
System.Net.WebException: Unable to connect to the remote server ---> System.Net.Sockets.SocketException: No connection could be made because the target machine actively refused it 10.24.4.111:8530
   at System.Net.Sockets.Socket.DoConnect(EndPoint endPointSnapshot, SocketAddress socketAddress)
   at System.Net.ServicePoint.ConnectSocketInternal(Boolean connectFailure, Socket s4, Socket s6, Socket& socket, IPAddress& address, ConnectSocketState state, IAsyncResult asyncResult, Exception& exception)
   --- End of inner exception stack trace ---
   at System.Net.HttpWebRequest.GetResponse()
   at Microsoft.UpdateServices.Internal.HealthMonitoring.HmtWebServices.CheckContentDirWebAccess(EventLoggingType type, HealthEventLogger logger)

It seems some service is still trying to connect to port 8530. Is it mandatory to use 80 or 8530 as the WSUS http port?