You try to copy and paste data from a webpage to a Microsoft Lync 2013 conversation window. The data is encoded by using the <fieldset style> tag. In this situation, nothing is pasted to the Lync 2013 conversation window.
This issue occurs because the HTML <fieldset> elements that have nonzero values for the z-index attribute in the webpage are ignored by Lync 2013.
To resolve this issue, install the following update:
2881070 August 2014 update for Lync 2013 (KB2881070)