I was poking around the resolver code, and found the following lines in FileURL.makeURL:
    String userdir = System.getProperty("user.dir");
    userdir.replace('\\', '/');
This is in org.apache.xml.resolver.helpers. These lines used to be in ResolvingXMLFilter.java in an older version of the resolver code. Unless reality has warped on me, the userdir.replace() call has absolutely no effect.