If you use /replaceitem command and you add sword to skeleton hand, then shoot you with sword. I tested it and the skeletons are shooting with every item. And the wither skeletons can't shoot with bow.
This bug is need to fix because skeletons with sword is can be part of custom maps.
1. /repair command and add an item to skeleton main hand.
2. /gamemode 0.
3. The seketon is shooting with an item.
4. repeat /replaceitem command with a witherskeleton and add a bow.
5. the witherskeleton is not shooting with bow.

Sorry I speak a little English and I used google translator.