I'm not sure about Mandrake. I know that SuSE uses the hotplug system. I think hotplug is a new (but standard) way to interact with hardware changes on the fly (I know the term has meant that for a long time, but this is linux specific). When the system boots, there is a phase called coldplug which is really just hotplug setting up hardware that is connected at boot time. The name of the program in charge is stored in /proc/sys/kernel/hotplug, and I think is normally /sbin/hotplug.
I don't know if I've been much help, I know that this is what my distro uses.
Something else you might want to check. Try
This will give you a list of all drives and partitions on your system. Try this with the USB in and out. If it really isn't being detected at all (as a drive), then there will be no difference.