wither skulls are not visible

when you summon a wither skull it is invisible

1:type this in a command block:/summon WitherSkull ~ ~2 ~-1

{ExplosionPower:10,direction: [4.0,0.5,1.-5] 2:}

2:build a wall of blocks in direction EAST
3:then you will se that the wither skull is there,but not visible

you can also download my save WITHER SKULL BUG