Blocks on armors stands don’t show

When using a command to add a block to armor stands head, the block doesn’t show on its head, but instead can be removed and be placed into the hotbar / inventory from said armor stand and still has its sound effect from removing 

This is the command I used 

/replaceitem entity @e [type=armor_stand, r=2] slot.armor.head 0 dirt

the only blocks that do work is normal pumpkin and carved pumpkin but nothing else 

( that I know of )