Edgeport/8i can send but not read - /4i works fine

Hi all,

I’m using an Edgeport/8i (301-1000-28) USB to RS-232 hub to communicate with some equipment. I can successfully send commands to my devices, and they react appropriately, but their responses are strings of 0x00. I know this isn’t a problem with my application, because I’m able to send and receive from the same devices if I use an Edgeport with only 4 ports. Running Windows 7 64-bit. Any ideas what’s going on here?