Yep! That's true! The 'front page' of Moodle is a 'course' in a way and it is the only backup you cannot restore. That's by design. It isn't an error. That does make sense to me considering users/roles and their permissions, etc. (authenticated user vs other users, etc.).
You'll have to ask the reasons why to Moodle.HQ folks if you want a technical answer.
'spirit of sharing', Ken