@Robert: I made some additional tests. I tried to reproduce the issue with two different colleagues (A=1440x900; B=1680x1050), but it crashed only with one of them (B).
Steps to reproduce:
1) Other party has to start a screen sharing session.
2) Click on the icon "Actual Size"(*)
3) Crash
Maximizing the window or the Icon "Fit to Screen" works fine.
Here is a screenshot: http://666kb.com/i/cny2ju2tigb0ocvet.jpg
(*) Actual size shows the content as it appears on presenter’s screen without scaling. This means if presented content is bigger than what can fit in your Lync window, scroll bars will be shown. ( Presenting your Screen with Lync 2013 - Lync Team Blog - Site Home - TechNet Blogs)