Testforblock Command. DataTag {Damage} in Item Structure is Tag Short?

Item Structure DataTag

it is Tag Short?
When I used command testforblock.

/testforblock ~ ~1 ~ dispenser 0 {Items:[{id:minecraft:skull,Count:1b,Slot:0b,Damage:2s}

Item in dispenser check it correct?!

and when I used command testforblock. change to Damage:2s to Damage:2b

/testforblock ~ ~1 ~ dispenser 0 {Items:[{id:minecraft:skull,Count:1b,Slot:0b,Damage:2b}

IT NOT WORK! T_T

It bug or not.
Please help. I suspect!