I used the command: "clear @a[nbt=\{HurtTime:1s}]" in a command block for a survival world so that taking damage would cause my items to be deleted - a fun little challenge - but I realized as I played that when an arrow shot by a skeleton is blocked with a shield, the items are removed anyway. I'm no expert but it seems to me as if this must mean that an attack blocked with a shield still registers a damage event, which I  would assume is not an intentional feature.