Respawned dragon doesn't have a health bar

When experimenting with the End, I summoned a second Ender Dragon using the clay Creeper face. Once summoned, however, there was no health bar to accompany the new Dragon

To Reproduce:
1. Go to the End and kill the Dragon
2. Create a Creeper face on the ground using clay blocks
3. Notice that a new Dragon is summoned, but there is no boss health bar