Mob spawn eggs broken

In creative mode, I put skeleton mob spawn eggs into a dispenser, then fire the dispenser, but get no mob. The dispenser does fire and puff, but there's no mob.

When using a dropper, you just get the egg back.

 

Also, even though the dispenser is firig (puffs of smoke) the quantity of eggs in it, does not change.

 

It does fire (normal) chicken eggs. But replacing them with mob spawn eggs, yields the above result.