Skeletons (without a bow) with an helmet will still hide in the shadow, Zombies with a helmet will not hide in the shadow.
Zombie AI was earlier updated and there are no problems with them.
But the skeleton AI is recently updates and there are issues with.

Command:

/summon Skeleton ~ ~1 ~ {Equipment:[{id:270},{},{},{},{id:298}],Attributes:[{Name:generic.maxHealth,Base:50}]}

I expected that the skeleton would try to attack me.
But he is somehow scared for the light while he has an helmet on his skull.
The Zombie with a helmet will try to attack you, the skeleton not.

1. This can be reproduce this with the command:

/summon Skeleton ~ ~1 ~ {Equipment:[{id:270},{},{},{},{id:298}],Attributes: [{Name:generic.maxHealth,Base:50}]}

2. Let the skeleton summon in the shadow
3. Go out of the shadow, then do gm 0
4. the skeleton will not walk to you to attack you.
(The Zombie will do that)