For the purpose of Pre-requisites, CL is not being calculated correctly. I noticed during my testing, that if I add 1 level of 5 different spellcasting classes (3 arcane and 2 divine) I qualify for Brew Potion, and Craft Magic Arms and Armor. It seems to hold for other item creation feats that need a minimum CL to get. I believe that the actual requirement is caster levels in 1 class, rather than spread (CL 1 in 5 classes) out like that.