Lync phone Polycom CX600, CX500 DSCP marking issue

We have Lync 2010 deployed with Polycom CX500 and CX600 as user phones.

We've configured "Set-CsUCPhoneConfiguration -VoiceDiffServTag 46" on lync management shell and reboot the phones. But the wireshark capture of the voice packets send out from the polycom phones shows no DSCP marking (The DSCP field is "00").

We even reboot the lync server, but still no help.  The problem happen on both CX600 and CX500.

Does I missed any configuration?

Thanks.