Hi Paul,
--I think you are using cross tab in that report. when you export that report into PDF it will Identify the next page and it will printed that report in the Next page of PDF defaultly.
--When use that report as sub report, then the main report treated that sub report as a single object and it will try to print that whole sub report at a time.
--Change the report in to Landscope mode and you need to increase the horizontal report size manually based on the number of horizontal columns.
Regards,
Naga.