Psygrammator

Your code is confusing class_index
 
Looked in the code, when adding a sub class, it assigns the desired index. You re-assign the index -1 to the skills.

try
// solo le enseniamos el skill si es que el mismo no lo tiene aun o si es el inferior al q le vamos a enseniar if (player.getSkillLevel(id) < level) { // Add the L2Skill object to the L2Character _skills and its Func objects to the calculator set of the L2Character player.addSkill(skill, false); }