The service is probably configured to restart on failure. This is why you don't terminate services from Task Manager. Killing the process there means it will not exit cleanly, which causes the service controller to interpret it as failed---and respond accordingly.
Either use the UI management console (services.msc) or the command line (net stop SERVICENAME).
If you insist on killing services using the wrong tool, you should set those services to "Take No Action" on first/second/subsequent failures in the service management console. There may still be events logged for abnormal termination, but the service controller will no longer restart the service.