Can someone explain the avatar skill tree rules?

[MCM]

I'm having a problem with my avatar skill tree. The quickest way to explain is to look at my skill tree below:



I cannot put a point in:

Melee Defense
Melee Attack
Speed
Charge
Armor

(if I click ANY of the above, nothing happens)

I can put a point in:

Fatigue Resistance
Morale
any of the other first-tier skills

What the heck is going on? Are there some secret skill tree requirements that the game doesn't display? The encyclopedia has 0 information on specific skills. What are the rules for putting skill points in?