Assume that the Call Forwarding or Simultaneous Ring setting is configured on a Microsoft Lync Phone Edition device. When you do call forwarding, the simultaneous ring to delegates feature can't be enabled.
A cumulative update is available that lets you re-enable the delegation setting from the Lync Phone Edition device instead of having to do this on a Microsoft Lync Front End server or a Microsoft Lync 2013 (Microsoft Skype for Business) client.
How to apply this cumulative update
To resolve this issue, apply one of the following cumulative updates, as appropriate for the telephone that you use: