Hi,
I'm using nano-x with that kernel version for 5475 and have seen something similar with the keyboard.
Do you see it by just having the mouse or other peripherals as well? I can trigger this with certain USB flash drives and it could be related to a potential USB1.1/2.0 problem in the kernel (check the kernel's bugzilla).
Are you just running OHCI or EHCI as well? Also, try another mouse or keyboard and see if the problem persists.
Good luck,
Andreas