When an adult mob is spawned from the spawn egg, the sound of that animal is played upon spawning. When baby animals are spawned via a spawn egg by clicking the dedicated mob with that spawn egg, this sound is not played. The bug is pretty self-explanatory but here's still some details:

What I expected to happen:

Spawning babies under an adult animal should, like spawning adult animals, play the sound of that animal (but pitched up because it's a baby). 

What actually happens:

No sound is played at all when a baby is spawned under an adult mob using a spawn egg.

Steps to reproduce:

1. Take a cat spawn egg and spawn a few cats
    Every spawned cat meows right upon spawning
2. Click with the spawn egg on one of the cats
    The spawned kitten makes no sound