Microkey Air 61 Power Struggle!

[MartieFuncum]

Can't figure out why my microkey air 61 won't power up with USB?

It's ok with batteries, and Bluetooth midi works fine with Korg Gadget. So why can't I power it with a USB AND use Bluetooth midi? Or is it designed so that if you attach USB you can only connect to to a device via USB (I use a Focusrite itrack Dock which I don't think is compatible with the microkey when attached via USB so the Bluetooth midi is a godsend!)

I've only tried to connect the microkey USB to a powered hub but not a PC as I won't be using a PC with it, just don't understand why it won't power up without batteries, no matter how many cables I try?