I have created a 2 step fix.

1) in my code where the frame with the chart/subchart is dynalically saved/loaded, I had to surround the ReadComponent call with GlobalLoading routines:

BeginGlobalLoading;
try
  MyFrame:=aStream.ReadComponent;
  NotofyGlobalLoading; // calls Loaded for all loaded components, including subcharts
finally
  EndGlobalLoading;
end;


2a) Secondly, I had to patch the TChartSeries.Loaded routine to not only look in the direct owner, but a bit further in the hierarchy as well:

Procedure TChartSeries.Loaded;
{$ifdef HH_PATCH_TC_GETDATASOURCE}
  function lclResolveDatasourceByName(const aName:string):TCOmponent;
  VAR O:TComponent;
  begin
    Result:=nil;
    O:=Owner;
    // try to find as component owned by one of the parent components
    while Assigned(O) and not Assigned(Result) do
    begin
      Result:=O.FindComponent(aName);
      O:=O.GetParentComponent;
    end;

    O:=Owner;
    // try to find as component owned by one of the owner components
    while Assigned(O) and not Assigned(Result) do
    begin
      Result:=O.FindComponent(aName);
      O:=O.Owner;
    end;
  end;
{$endif}
var t : Integer;
begin
  inherited;

  { when the DataSource has multiple Series, load them... }
  if Assigned(FTempDataSources) then
  begin
    if FTempDataSources.Count>0 then
    begin
      DataSources.Clear;
      for t:=0 to FTempDataSources.Count-1 do
{$ifdef HH_PATCH_TC_GETDATASOURCE}
          InternalAddDataSource( lclResolveDatasourceByName(FTempDataSources[t]) );
{$else}
          InternalAddDataSource( Owner.FindComponent(FTempDataSources[t]) );
{$endif}
    end;

    FTempDataSources.Free;
  end;

  { finally, gather points from datasource after loading }
  CheckDatasource;
end;



2b) And I patched the TChartSeries.IsDataSOurceStored to always return False so it will always use the Dataseources property to store datasource links, while still maintaining backwards compatability for existing forms.