I retested this here with:
procedure TForm1.Button1Click(Sender: TObject);
begin
AdvGridExcelIO1.GridStartRow := 2;
AdvGridExcelIO1.GridStartCol := 2;
AdvGridExcelIO1.GridEndRow := 50;
AdvGridExcelIO1.GridEndCol := 5;
advgridexcelio1.XLSExport('e:\tms\temp\subset.xls')
end;
and this exports the desired subset of cells to the xls file.
So, it is unclear how this behaves different for you.
If the problem persists, can you isolate & send a sample source project with which we can reproduce this here?