Documentation: Next arrow in the index page opens invalid page

The "Next" arrow in the index page (http://docs.jboss.org/drools/release/6.1.0.Final/optaplanner-docs/html/index.html) opens an invalid page (http://docs.jboss.org/drools/release/6.1.0.Final/optaplanner-docs/html/pr01.html).
The same issue happens when clicking the "Prev" arrow from the Chapter 1 page (http://docs.jboss.org/drools/release/6.1.0.Final/optaplanner-docs/html/plannerIntroduction.html).