USB Passthrough not working for Windows 7 guest

USB Passthrough from host to guest is not working for a 32-bit Windows 7 guest, while it works perfectly for a 32-bit Windows XP guest. 

The device appears in the device manager of Windows 7, but with "Error code 10: device cannot start". I have tried this with numerous USB thumbdrives and a USB wireless NIC, all with the same result. The device name and functionality is recognized, so at least some USB negotiation is taking place.

I am trying this with the latest git-pull of QEMU-KVM. 

The command line to launch qemu-kvm for win7 is:
sudo /home/user/local_install/bin/qemu-system-x86_64 -cpu core2duo -m 1024 -smp 2 -vga std -hda ./disk_images/win7.qcow -vnc :1 -boot c -usb -usbdevice tablet -usbdevice host:0781:5150

The command line to launch qemu-kvm for winxp is:
sudo /home/user/local_install/bin/qemu-system-x86_64 -cpu core2duo -m 1024 -smp 2 -usb -vga std -hda ./winxpsp3.qcow -vnc :0 -boot c -usbdevice tablet -usbdevice host:0781:5150

Any help is appreciated.