In testing this for comparison purposes, I have found an indication of what may be behind this problem:
On nvidia chipsets, this problem occurs. (In my case, nvidia's MCP61 chipset with the ohci_hcd and ehci_hcd drivers)
On Intel chipsets, this problem does not occur. (Test case is Intel Corporation 82801JI (ICH10 Family) controllers with the ehci_hcd an duhci_hcd drivers)
On the Ubuntu-users discussion list, this has now been confirmed by another user.
In testing this for comparison purposes, I have found an indication of what may be behind this problem:
On nvidia chipsets, this problem occurs. (In my case, nvidia's MCP61 chipset with the ohci_hcd and ehci_hcd drivers)
On Intel chipsets, this problem does not occur. (Test case is Intel Corporation 82801JI (ICH10 Family) controllers with the ehci_hcd an duhci_hcd drivers)
On the Ubuntu-users discussion list, this has now been confirmed by another user.