A skeleton, who currently is not targeting the player, but targeted by an iron golem or wolf will just stand there, even if wielding a sword too, and makes no attempts to retaliate/fight back, not even shooting an arrow, and will just stand there getting knocked back and hurt repeatedly.

I know zombies were already like this way before, the skeletons seem to have changed after the 1.4.3/1.4.4 update.
Spiders and pigzombies still fight to the death.