When placing any mob heads in dispensers they don't dispense.
the item count does not go down or item dispensed.
Issue can be see in this gfycat.
Linked issues
is duplicated by 4
relates to 2
Comments 8

But Zatherz is right, since Dispensers were changed to place wither skulls (= heads) to build a wither, the wont fire out any kind of head any more.
ah ok sorry that does make sense then... 😞 but that breaks a lot of historic maps.. ok so use dropper instead.
ok thanks for the confirmation.
This is still an issue and is not intended. https://mojang.com/2014/01/minecraft-snapshot-14w04a/
I would love to see this bug fixed.

What exactly is not intended ?
He thinks that since they can be dispensed to build golems, they should be able to be dispensed as blocks. I disagree. Either all blocks should be dispensable (as blocks), or none of them, not some and not others.

It would be nice if the base of the golem doesn't exist, the dispenser drop the skull.
S0, check for golem- If golem all there, make golem. If golem partly there, drop head. If golem not there, do nothing?
That seems like a terrible idea. Consistency is good.
Dispensers don't normally place heads Dragnoz, they can place wither skulls/pumpkins when the base of the golem is actually built.