Probably the USB hub is either unpowered, or perhaps underpowered.  Bluetooth devices require power from the USB port, so the fact that it works while directly connected but not when connected to the hub is a pretty good clue.  You didn't mention what else you are connecting to the hub, but since they are working I suspect they either don't require power, or require very little.  Pick up a powered hub, one that you actually plug in to a power strip, and I bet the problem goes away.