trying to break a mob or player head with a tool that has the tag "CanDestroy" and the correct head selected fails to break the block

 

example. I have a golden shovel with the tag 

{CanDestroy:["minecraft:wither_skeleton_skull"]}

when I try to break a wither skull, it doesn't work.

 

full command used for shovel:/give @p minecraft:golden_shovel

{CanDestroy:["minecraft:wither_skeleton_skull"],Damage:31}

I can put other blocks in place of "wither_skeleton_skull" and this works fine.

 

update:my mistake, skulls on the wall and skulls on the floor are two different blocks