Wither Skulls don't spawn properly

When using the command "/summon WitherSkull ~ ~ ~

{direction:[0.0,0.0,0.0],ExplosionPower:0,CustomNameVisible:1,CustomName:"test"}

"

a Wither Skull named test should spawn. However the command block output says "Unable to summon object" this command worked in the previous version.

I hope this isn't intended as it is extremely useful for Redstone contraptions.