In Report Writer, iSolved allows for Heading1 and Heading2 for each column. If both of these fields are populated with titling information for the column, you'll have two header rows when you take the report into Excel. This is useful if you have particularly long column heading information and are worried about the column width for a report you're taking to PDF, but it can get annoying if you're trying to filter the information once you get into Excel.
If you'd prefer to only have one header row, simply make sure that each column (in Edit Columns) only has text in either Heading1 or Heading2. It doesn't matter which you use, as long as you're consistent.