i think the special skills release the oportunity of adding points (and activiting them) by lv pr tiers.
I mean; i couden't do Evade until lv20, now i'm lv 20 but i can only put 2 points in them; and i need to be lv 30 to be aible to add more skill points, then i think i will be aible to put another 2 or 3 points until tier5 and so on.