If you spawn a skeleton riding a spider it doesn't have a bow and doesn't use a ranged attack, he just hits you like a zombie. I know this is just a snapshot but I thought I would mention it. Also it may also affect 13w37a, but I haven't tested that.
MC-30931
Skeleton Spawned Riding On Spider using /summon doesn't have bow and attacks like a regular mob.
Resolved
Invalid
0
This is not a bug. This occurs because when skeletons spawn naturally, their NBT data says they are holding a bow. If you were to edit the command to have the skeleton be geared with a bow, they would attack by shooting as normal.