According to this Apple Document: http://support.apple.com/kb/HT5172#8
"How do I get the best performance from the USB 3 ports?
The first device you plug in will configure the port, so always connect USB 3 capable hubs or devices first.
What happens if I plug in a USB 2 device into the USB 3 port first?
If you plug in a USB 2 hub first, all devices connected or "daisy-chained" to that hub will operate up to the maximum transfer rate of USB 2 speed (480 Mbps)."
I'm hunting around here to see if there is apossibility to reset this without restarting the Mac...