Unable to /summon Fireball

When attempting to /summon a Fireball, Minecraft presents me with the error message of "Unable to summon object." I am able to summon any other entity. Even when I add the direction tag to the fireball, it continues to not summon.

Steps to Reproduce:
1. Download and open Minecraft 15w33b.
2. Open a Minecraft world with cheats enabled.
3. Type in chat: "/summon Fireball" or "/summon Fireball ~ ~ ~

{direction:[]}

4. Notice how the chat displays the message of "Unable to summon object" in red text.

Confirmed in 15w33b.