Consider the following scenario:
You deploy the Response Group Service (RGS) in a Microsoft Lync Server 2013 environment.
You assign several agents to a Response Group.
A user makes a call to the Response Group. Then, all Lync clients of the agents ring.
One of the agents answers the call.
In this scenario, the clients of one or more other agents still ring and receive the toast notifications.
To resolve this issue, install the following update:
2938505 Update for Lync Server 2013: April 7, 2014