Unobtainable Spawn Eggs Still Disappear in Dispenser

I know it is intended for some spawn eggs to be unusable, but this is different!

First give yourself an unusable spawn egg like a giant spawn egg with the command '/give @p minecraft:spawn_egg 1 0 {EntityTag:{id:"Giant"}}'. Then place it in a dispenser. Activate the dispenser with redstone and as intended no giant will spawn BUT the spawn egg will disappear anyway.