Does the architecture of the Compute Module (when mounted in a Compute Module IO Board) support simultaneous USB host and device/client port operation? This post suggests that a BeagleBlack Bone board is more suitable (because previous RPi only allowed host or device, but not both at the same time).

As a simple experiment, I tried connecting the USB host port to the slave port on the CMIO board (via a hub that also had a wi-fi adapter)-- this seemed to disrupt the entire USB (disconnecting all devices) until the slave port was disconnected.