Giants do not get damage when hit by Instant Health

What I excepted to happen was:
Giants get harmed when throwing Instant Health to them. (Because undead get harmed)

What really happened was:
Giants were healed.

Steps to reproduce:
1. Spawn a giant. (Do not ask how)
2. Throw an Instant Health at him!
3. ....
4. Giant did not get harmed or lose health.