This issue occurs when a USB audio device, such as a Polycom CX600 telephone, is paired to a computer that is running Microsoft Skype for Business (previously named Microsoft Lync 2013). This issue occurs because the focus is on the hang-up button in a call in Skype for Business or Lync 2013. This is by default.
Note This issue does not occur if the default audio device for a Skype for Business or Lync 2013 client is a headset.
To resolve this issue, install the May 12, 2015, security update for Skype for Business.
Note Microsoft Lync 2013 was upgraded to Skype for Business in April 2015.
The third-party products that this article discusses are manufactured by companies that are independent of Microsoft. Microsoft makes no warranty, implied or otherwise, about the performance or reliability of these products.