No sound from SC-55 when controlling with A-500 Pro

The audio output on the SC work fine, as I have tested the sample songs. It just looks like there is no MIDI input from the keyboard into the module. I would think that at least simple note MIDI messages would be transmitted, but this doesn't seem to be the case. Note that the keyboard is being powered by the USB, so maybe this means it shuts off its MIDI outputs? I don't see why that would be the case. Anyone know how to fix this problem?