That's what I thought. However, the stored procedure above clearly produces just one resultset at any time. It is impossible for the SP to actually produce two resultsets. Or are you saying, that somehow SQL Server does not care about the IF and therefore there are two resultsets.
Btw we tried limiting the number of resultset manually in the designer using the context menu. This did not work. Clicking on "1" to limit to a single resultset did not have any impact.