github.com recently added the ability to checkout a git repo with subversion with a URL such as
http://svn.github.com/doctrine/doctrine2.git

(see http://github.com/blog/626-announcing-svn-support)

If this URL is specified in a Husdon job configuration, it will never checkout the code. A manual svn co http://svn.github.com/doctrine/doctrine2.git does work.

I tried browsing the URL manually in the web browser and it returns 'incomplete headers' so it is possible it's only accepting traffic from know subversion clients, or only responds to specific subversion commands rather than http commands. In any case, the Husdon subversion plugin cannot checkout repositories hosted at github.com