Some commands in the Command Blocks aren't working!

I got on the new Snapshot of 14w06a the day it got released and tried to get a customized player head by the code /give 397 1 3

{SkullOwner:MHF_Pig}

and clicked done. I decided to put a button on the Command Block and clicked.
What I expected to happen was that the command block would've given me a Pig Player Head but instead nothing happened when I clicked on the button.
I tried to do another /give command but with a dandelion with modified attributes. (Command was /give @p 37 1 0 {AttributeModifiers:[

{Operation:0,UUIDLe­ast:1,UUIDMost:1,Amount:100,AttributeNam­e:generic.attackDamage,Name:Flower}

],dis­play:{Name:"Dandelion of Death"}} ) This time I put a pressure plate on top of the Command Block and I stepped on it, but it gave me nothing. I used redstone dust, redstone torches, and redstone blocks also, which all didn't work for me.
Though the new /give @p stone 16 0

{CanPlaceOn:["minecraft:diamond_block"]}

command worked, it gave me the stone in my inventory instead of my hotbar when I had all empty spaces in it.

Some steps to reproduce this issue.
1. Place a Command Block
2. Put a custom player head or modified attribute command in it. (Edit: Checked some other commands, they worked)
3.Click Done and try to power the Command Block.