[Samba] rsync folder permissions

[steve]

I'm trying to rsync our filserver to a USB backup. When I first start, 
all the folders are created with
  root:root
ownership whereas the actual owners are
  root:Domain Users
or
  root: one.of.our.groups

Eventually, the groups show correctly, but not always. My question is, 
when rsync creates the new directories, does it respect user and group 
all the way along or must we wait for the end of the rsync to find out?

IOW, sometimes we get a correct rsync but not every time even if we 
leave it to the end.

If anyone can help me with the English here that would be beautiful.

Cheers,
Steve