Cannot Add/Move/Delete Contacts in Lync for Mac

Our Mac users are reporting that they cannot add, move, or delete contacts in Lync for Mac:

• When they try to add a contact in Lync to a group (i.e. Other Contacts or Pinned Contacts), nothing happens. 
• When they try to move a contact between groups (i.e. Other Contacts or Pinned Contacts), nothing happens.
• When they try to delete a contact, nothing happens. 

When the users use Lync through Outlook Web App or Lync 2013 for Windows, they are able to successfully add/move/delete contacts. 

We are all running the latest version of Lync for Mac 2011 (14.0.7)

Help?