Consider the following scenario:
You deploy the Enterprise Voice feature in a Microsoft Lync Server 2013 environment.
You configure the IP private branch exchange (PBX) gateway to fork an incoming public switched telephone network (PSTN) call to an IP telephone and a Lync client.
You configure two users (user A and user B) in the environment.
User A makes a PSTN call to user B. Then, the IP telephone and Lync client of user B are ringing.
User B answers the call by using the IP telephone.
In this scenario, user B receives an incorrect missed call notification in the Lync client.
This issue occurs because Mediation Server deals with the SIP reason header incorrectly, and then generates a missed call notification.
To resolve this issue, install the following cumulative update:
2937310 August 2014 Cumulative Update 5.0.8308.738 for Lync Server 2013 (Front End Server and Edge Server)