A 157
1. It only counts the actual enhancement bonus, not the special properties. A +2 Merciful sword requires only CL 6, even though Merciful is a +1 enhancement. Of course, a +2 Flaming sword still requires CL 10, since Flaming requires CL 10 on its own. However, you count all of the final weapon requirements. Merciful on its own only requires CL 5, but improving a +2 weapon to a +2 Merciful weapon requires CL 6, since +2 requires CL 6.
2. This is only a guideline as to how to create magic items beyond those printed in the books. Ignore this when considering existing special properties, such as flaming.