Hitbox for child mobs error when growing up

Mods (chicken, shhep, pigs and cows) dies when growing up if they comes in contact with another mob (parent)
I have 2 pigs in a 2x2x2 cell, when breeding them, all is well until the moment the child grows up, if it comes in contact with another pig it get damaged, and dies. Same goes for all 4 types of mobs.
if the cell is bigger the same happens, it just takes more time before they collide (walking past eashother is often enough).
Seems like the hitbox for mod have an error when the mob growes up (there "damage" box is grown up, but the "limit" of theyr bodies have not, if that makes sense).
Bug was not pressent in 13w05, but from 13w06 it have been pressent.
if mob child are removed from parent before growing up, it will live (in most cases) provided is is alone (sometimes contact with walls will kill them).
Grown mods created with 13w05 or earlier is not affected.