spice-client 0.8 requires spice-usb-share 4.9 (already in RHEL-6) to share USB devices correctly. See also bug 681537.
Technical note added. If any revisions are required, please edit the "Technical Notes" field accordingly. All revisions will be proofread by the Engineering Content Services team. New Contents: The spice-usb-share package has been upgraded to version 4.9, which ensures that USB devices are shared correctly with SPICE client 0.8.1.
Verified on kmod-kspiceusb-rhel5u6-4.5-8.el5 spice-usb-share-4.9-10.el5 spice-client-0.8.1-6.el5 (in both fullscreen and window mode) Did multiple writes of 100M file and checked md5sum. Everything seemed to be allright.
Since the problem described in this bug report should be resolved in a recent advisory, it has been closed with a resolution of ERRATA. For information on the advisory, and where to find the updated files, follow the link below. If the solution does not work for you, open a new bug report. http://rhn.redhat.com/errata/RHEA-2012-0174.html