On my XP Pro system, my Remote Desktop Service, is still set to Manual and it is running and I have never had the problem of the Avast UI not starting. Why this is so on my system I have no idea but for some it has been an issue the setting is a workaround as it is a required service.

For some reason unknown to me (an avast user) this service doesn’t start when requested by avast on some systems. It is entirely your choice to start it automatically as a workaround or not.