When I summon a Shulker in 15w33b with NBT Tag "Peek" [/summon Shulker ~ ~ ~

], it only opens like

. I was testing this command in 15w31c and it works. I think is a bug, but if it's not a bug, it's my mistake.
In the first image it's the Shulker with NBT Tag "Peek" with 99 in 15w31c, and in the second image, is the same world with another Shulker with NBT Tag "Peek" with 99 in 15w33b

[FIXED in 15w33c]