We recently made a change to the Lync 2013 client to support the ability to fall back to the Lync Web App in the event that a user has Lync installed but has never signed in. This was frequently a challenge because various versions of Office 2013 come with Lync 2013 installed by default. There are ways that IT pros and administrators can control this however many installations include Lync 2013 by default.
The change was first introduced in Lync 2013 version 15.0.4623.1001 so if you install any version that was released after that your Lync client will contain this change. You can find a link to the most recent Lync updates at the following URL: http://technet.microsoft.com/en-us/office/dn788954.aspx.