There is a bug in the usb stack. Try the following sequence. You need one
usb hub and two usb devices. First, connect the usb hub to a usb port.
Make sure devu-ohci/devu-uhci is running. Then insert device 1 into the
first port of the hub. Then insert device 2 into the second port of the
hub. If you have the “usb” utility, run that on the command line to see all
usb devices. Now, on to the bug. Disconnect device1 and reinsert it into
the first port of the hub. Then disconnect device 2 and reinsert it into
the second port of the hub. Now, device 2 is no longer recognized. Type
“usb” and it will tell you “No such device” on device 2. You can remove and
insert device 2 into the same port as much as you want but you won’t be able
to see it anymore. If you swap device 1 with device 2, you’ll be able to
see device 2 but not device 1. To fix this problem, the hub has to be
disconnected and reconnected so that all devices could be renumerated.