Microsoft has released a new Cumulative Update for Lync 2013 Client couple days ago. This fix addressed bunch of issues including,

• Presence status isn’t updated based on Exchange calendar in Lync 2013
• You can’t drag a contact from Lync 2013 to another application
• Proxy authentication dialog box appears when you sign in to Lync 2013

Note that once updated, there is a known issue with this fix.

• Screen readers cannot read aloud keystrokes during a Lync 2013 application or desktop sharing session in Windows

Before applying the CU Update, Verify that below prerequisites are installed.

• MSO (KB2727096)
• MSORES (KB2817624)
• IDCRL (KB2817626)

You can download above patches and the CU update from http://support.microsoft.com/kb/2825630