Hi Ram,
Yes, you are right. This is a Lync for Mac 2011 client issue, and I notice that you are using Office 365 Enterprise after upgrade tenant.
This issue occurs because, when the Unified Contact Store is deployed between Microsoft Exchange 2013 and Lync Server 2013, the Lync 2010 and Lync for Mac 2011 clients do not understand where it should update or save changes. Therefore, users who are enabled for the Unified Contact Store cannot change their contacts list from Lync 2010 and Lync for Mac 2011.
And in this situation, I suggest you use Microsoft Lync 2013, Microsoft Outlook Web Access 2013, or Microsoft Outlook to change your contacts.
More information for your reference: http://support.microsoft.com/kb/2757458
Thanks,
Bourne Zhang
