Passives Tree Malfunction??

Hey everyone! I just started up this season after not playing since 0.2. I'm a level 16 monk, and I'm going down the offensive start to the tree. However, I've run into an issue where I can't invest points into nodes adjacent to nodes I've already unlocked. Is there something I'm missing that I need to unlock that I'm forgetting? Some adjacent nodes are orange and let me spend; other adjacent nodes have the orange line going up to them but are gray around the node and don't let me spend.