This might not really be a bug perse, but the baby zombies, are very hard to defeat, for they come at you much faster then you can outrun/defend/attack them.

Other mobs on the other hand are balanced enough (despite they run at you now) so far to tactically fight them, yet the baby zombies are way to fast and difficult to hit, and when hit, they do to little damage.
And this get very frustrating as holding a shield blocks the sight of them too.