How many USB devices I can connect to MOX

I have MOX classic with one USB port, but I need to connect more devices than one, so I used 8 port USB hub , but when I connect anything to that hub MOX says (dmesg):

xhci-hcd d0058000.usb: Error while assigning device slot ID
xhci-hcd d0058000.usb: Max number of devices this xHCI host supports is 4.
usb 2-1.1-port2: couldn’t allocate usb_device

are there any limitations?

p.s. I use 8 port USB hub with Omnia and everything works fine.