Symptoms
Assume that you open a group chat window in Microsoft Skype for Business 2015 (Lync 2013), and then you click the Search button in the lower-left corner of the window to open the Search Chat Room History dialog box. In this situation, you find that the dialog box has too many controls and it pushes the OK and the Cancel buttons off the visible bottom.
Resolution
To fix this issue, install the February 7, 2017, update (KB3161988) for Skype for Business. Note Lync 2013 was upgraded to Skype for Business in April 2015.