Mitel had us verify that the 2nd DHCP server was not assigning the vlan, as apparently there is an issue with 5.0 that if the vlan is assigned on both requests (even the same vlan), this can happen. This of course assumes that you are running a separate voice vlan. The phone requests an address via DHCP, the DHCP server gives it a "normal" IP, and assigns a vlan (say 800), the phone then releases the address, then re-asks for DHCP on vlan 800. If the DHCP server on vlan 800 also supplies the option (either in option 43 or 125) and tells it 800, apparently the phone keeps switching vlans around, and can cause this issue.
However, with us, this is not the case. The DHCP server on vlan 800 does not re-iterate that we're talking on vlan 800.
Also, we're using option 43 in DHCP to assign l2p, diffserv, callserver, and tftp server. This is via a Linux ISC-DHCP server. We formulated the string by configuring an MXe-II for DHCP, then just copying the string to the Linux server.
We could probably live with the excessively long HTML App Upgrade times, but that other campus where it NEVER leaves that screen is a bit much. It must be doing something odd for that Upgrade, which its timing out on, or something silly. Will be messing with it more today to get those other 100+ phones on that campus working properly.