This issue occurs on the video locked attendee participant running Microsoft Skype for Business using Citrix RealTime Optimization Pack 2.0 when video hard mute is triggered in the conference.
When this issue occurs, the position and the size of the video rendering region are displayed incorrectly. Additionally, the position and the size of the video rendering region can’t be adjusted by any resizing of the conversation window.
To fix this issue, install the March 8, 2016, update (KB3114831) for Lync 2013 (Skype for Business).
Note Lync 2013 was upgraded to Skype for Business in April 2015, and Citrix RealTime Optimization Pack 2.0 requires the Skype for Business client.