After running the client in a "group chat", it doesn't appear to remove users that have left the group chat, so when they reconnect they come back and it duplicates the user's name on in the user list on the right hand side.
No --debug log provided by reporter, thus reducing priority
Please retry with commit 935fb65. I'm not sure if this will fix it, but I also can't reproduce the situation, because I only have one Lync 2013 persistent chat account.
No feedback from reporter. Assuming to be fixed by upcoming 1.17.0 release