A Microsoft Lync window stays on top of other application windows after you click another window to try to make it active. This problem occurs when two or more of the following conditions are true:
Lync 2010 is installed.
Lync 2013 64-bit is installed.
A third-party application that uses Lync is installed.
To work around this problem, use one of the following methods:
If you have both the Lync 2010 client and the Lync 2013 64-bit client installed on the same computer, remove the Lync 2010 client.
If you have a third-party application installed that uses the Lync client, remove the third-party application, and then verify that the problem is resolved. If the problem is resolved, contact the vendor of the third-party application for a resolution.
Microsoft has confirmed that this is a problem in the Microsoft products that are listed in the "Applies to" section.