CGAL does not accept that the polygon (exterior) ring touches itself. This is accepted by most other libraries. However, it is a reasonable choice. Therefore, the resulting area of CGAL intersections differs.

http://geometrylibrary.geodan.nl/for_osgeo_wiki/uscounty_cgal_problem_51191.png

There is also one polygon which is not accepted by MS SQL Server 2008.