The problem about AS download

Hi

I'll try to download a project to the device FPGA EP2C15AF484.The problem is that if I download the .sof file of the project by JTAG ,it is fine. But if I download the .pof by AS ,it can be downloaded but cannot run as I wish.If I convert the .sof file to .pof file and download it by AS,it runs as I wish too.

How can I do to download and run the original .pof file without converting?

Thanks.