We recently replaced our Cisco WLC and AP's with Meraki MR46's. Since doing this our 8821 phones will go into preservation mode ONLY on 3 of the 5 AP's. When you call into the phone you are able to establish the call on both ends. When the person with the 8821 walks down the hall and roams to one of the 3 AP's the person on the other end of the 8821 gets dead air, but the person on the 8821 can hear the other person. The phone will eventually go into preservation mode and the 8821 will unregister from the Call Manager. If you roam back to one of the 2 working AP's, the call will re-establish and both parties can hear each other.
Attached is a full debug of an instance of this happening with details of the call.
