Baby zombies show burn animation under lava but don't get hurt

When a baby zombie is placed in a space that is one block high and has lava directly above it, it shows the burning animation but does not get hurt or die.

Steps to reproduce:
1. Make a room with walls 2 blocks high.
2. Fill first layer with signs or other blocks that stop lava.
3. Spawn baby zombie in the room.
4. Fill second layer with lava.
5. Watch zombie burning but not dying.

In 1.6 they die in the same setup (which is expected because of the change in height of baby zombies) and they also die in 1.7 when put in lava or fire. Also, baby villagers are not affected.