In latest snapshot I see an exception (see text below) if you accidentally moving connecting node for some pixels.
P.S. if you press on the second node for some more time and then move it, error won't be displayed.
Uncaught exception: Exception caught: (TypeError) : Cannot read property 'ai' of null Caused by: (TypeError) : Cannot read property 'ai' of null | Uncaught exception: Exception caught: (TypeError) : Cannot read property 'ai' of null Caused by: (TypeError) : Cannot read property 'ai' of null