Baby zombies don't burn in sunlight

I was playing a new survival world on 1.7.9 and a baby zombie came out of the cave. since I didn't have a sword yet i decided to try and avoid it and let it burn in the sunlight.

Then the baby zombie followed me and it didnt burn i thought maybe it was to dark because i was under a giant jungle tree, so i went find and open area and found a desert nearby so i go into the desert and the baby zombie still didnt burn. Then i went on to creative and tested it multiple times and normal zombies burned like they should but the baby zombies still didn't burn

Steps to Reproduce:
1. Place a baby zombie in sunlight