sorry (duh) yep, it's the order() fn.  Wrt the fn, you'll obviously not want to break the hierarchy (ie don't use Bdesc or Basc) and if you have a numeric key or a sort column (put in as member prop) this could make it easier to do the sort.

if the members are all sorted OK in another querying tool, I would start to be concerned that it could be the matrix control in RS.  Does it have any specific sorting properties that could be defaulted and working against you?