Could you be more specific about what you're doing to see this problem? Are you viewing the demo on my server or yours, or locally on your machine? If not on my server, what version of Graphviz did you use to generate the xdot files, and what version of Canviz are you using? Are you viewing the standard Graphviz demo graphs or different graphs?
matches[2] should not be undefined, if the file Canviz is processing is an xdot file generated by Graphviz. Could you show me the xdot file that causes the problem?