Problem with USB2 storage devices, repeated kernel messages

Ever since Hoary I have been unable to mount USB 2.0 flash memory drives as usual. My USB 1.1 drive works as
expected. I'm on a Thinkpad t40, and a quick boot into Knoppix, where everything works, assures it's not a
hardware problem. I've run into this problem on a dist-upgraded Warty->Hoary install, a fresh Hoary install and a
fresh Kubuntu install, all fully updated to 04/19. I have tried 386, 686 and 686-smp kernel versions 2.6.10-3,
2.6.10-5 and 2.6.11-1. The only
difference being that 10-3 shows:

"usb 4-{3,4}: new high speed USB device using ehci_hcd and address ?"

once and does nothing, 10-5 repeats the message with increasing addresses until it is removed:

...
Apr 19 01:40:10 localhost kernel: usb 4-4: new high speed USB device using ehci_hcd and address 25
Apr 19 01:40:19 localhost kernel: usb 4-4: new high speed USB device using ehci_hcd and address 62
Apr 19 01:40:19 localhost kernel: usb 4-4: new high speed USB device using ehci_hcd and address 64
Apr 19 01:40:20 localhost kernel: usb 4-4: new high speed USB device using ehci_hcd and address 67
Apr 19 01:40:23 localhost kernel: usb 4-4: new high speed USB device using ehci_hcd and address 80
Apr 19 01:40:27 localhost kernel: usb 4-4: new high speed USB device using ehci_hcd and address 94
Apr 19 01:40:30 localhost kernel: usb 4-4: new high speed USB device using ehci_hcd and address 108
Apr 19 01:40:31 localhost kernel: usb 4-4: new high speed USB device using ehci_hcd and address 111
Apr 19 01:40:32 localhost kernel: usb 4-4: new high speed USB device using ehci_hcd and address 112
Apr 19 01:40:32 localhost kernel: usb 4-4: new high speed USB device using ehci_hcd and address 114
Apr 19 01:40:37 localhost kernel: usb 4-4: new high speed USB device using ehci_hcd and address 9
Apr 19 01:40:40 localhost kernel: usb 4-4: new high speed USB device using ehci_hcd and address 19
Apr 19 01:40:42 localhost kernel: usb 4-4: new high speed USB device using ehci_hcd and address 27
Apr 19 01:40:44 localhost kernel: usb 4-4: new high speed USB device using ehci_hcd and address 35
Apr 19 01:40:44 localhost kernel: usb 4-4: new high speed USB device using ehci_hcd and address 36
--- Unplugged and plugged into another port ---
Apr 19 01:40:51 localhost kernel: usb 4-3: new high speed USB device using ehci_hcd and address 54
Apr 19 01:40:52 localhost kernel: usb 4-3: new high speed USB device using ehci_hcd and address 59
--- Unplugged ---
and 11-1 usually does what 10-3 does with the occasional oops.

Manually modprobing scsi modules and usb-storage does nothing, neither does loading and unloading ehci_hcd and
uhci_hcd in various orders.

Any ideas would be greatly appreciated.