Does the Print ... dialogue provided by your printer driver include the option to "Choose paper source by PDF page size"?
If not, then it is perhaps likely that driver paper source selection over-rides the sizes embedded within the PDF document.
You could also check just what the print stream generated by your driver is instructing the printer to do, by capturing the stream to a file (use the "Print to file" option in the Print dialogue), then analysing the captured print job.
If the driver is a PCL5 or PCL6 one, you can do this analysis using the PRN File Analyse tool in the PCL Paraphernalia application, available via http://www.pclparaphernalia.eu