So I ran into the same issue. I have 8.6(2) and I installed the Device Pack and the latest .cop file (of course restarted TFTP) and the DX650 would not register. So I restarted the Cisco Tomcat (to get the icon's to appear), then restarted the Call Manager service and the phones registered right away.
I think even though you load the .cop files its not in active memory until the CM service is restarted. Hope that helps
