Windows 7: USB Port Changes to Low Speed After Sleep

After bootup, my high-speed USB devices are all connected to "Enhanced" Host Controllers and appear to work correctly at USB 2.0 data rates. When my computer awakes from "Sleep" mode, I get one or more of the messages that "This USB device can perform faster if you connect it to a HI speed USB 2.0 port." When look at the status of my USB Host Controllers, I find that my high-speed USB devices are now listed under "Universal" Host Controllers (rather than "Enhanced"), and, I assume, they are operating at USB 1.0 data rates. Can anyone explain why my USB devices change from "Enhanced" (USB 2.0) to "Universal"(USB 1.0) host controllers after Sleep and, more importantly, how to keep this from happening? When I reboot, everything changes back to normal, and the high-speed USB devices are again listed under the "Enhanced" host controller. Any help would be appreciated.