Devices won't share USB root hubs

After a great deal of angst and time, I discovered quite by accident that my
Maxtor Personal Touch 3100 external HD does not play nice with other devices
on a 2.0 root hub. (First rule of troubleshooting a USB device: try it with
no other USB devices plugged in. ::head desk: The moment I plug it in,
any devices that draw power from the hub (mp3 players and memory cards) quit
working.

It would seem to be a power issue, but the Maxtor drive has its own power
source. It will share 1.0 root hubs with no problem, and I plugged in a
couple of mp3 players and an SD card (without the Maxtor drive), and they
shared the 2.0 root hub with no troubles.

I'm a bit curious as to why this is happening - it's not really a problem,
since I was thinking of buying another external drive to backup the Maxtor,
and for the moment, I can work around it by disabling the USB 2.0 controller.