I was able to reproduce with our screen sharing demo.
Sounds like a WebRTC bug to me. However, I did note that Muaz's desktop capture demo works on a machine without a camera, so the alternate API using a chrome extension isn't affected. I've sent him a query asking about a particular issue I don't quite understand before I try to integrate it in (ideally, I'd like any easyrtc developer to be able to simply use an extension we put up on the chrome webstore rather than everybody having configure and upload their own).