This really affects v0.13.1 but for some reason the ''Affects Version/s'' box does not have that as an option. Anyway, to the bug. When a small mob such as Silverfish or Baby Wolves attack a Skeleton, the Skeleton has trouble shooting the mob because it shoots slightly to his left, therefore missing the mob almost always. As another bug (that I presume has already been reported, so I am not reporting it) stops Baby Wolves attacking Skeletons, a Skeleton will keep on firing at the Wolf, always missing, forever.
How to recreate:
1) Make a 4x4 block room.
2) Spawn a Skeleton in the room.
3) Spawn a Baby Wolf in the room.
4) With any luck, the Skeleton will start to fire at the Wolf when it attacks it and it will nearly always miss.