Lines 496-497:

# Toggles whether or not right clicking mobs with a milk bucket turns them into a baby.
milk-bucket-easter-egg: true

Right clicking them with a milk bucket does not convert them to babies.
Left clicking does.

This either needs to be fixed by editing the comment to say left click, or editing code to make it look for a right click.

This was fixed by 37acdc1 and is present in any recent version. (Thanks to @triagonal for the heads up.)