zombies die when falling from height in 23 or 24 blocks instead of keeping 1/2 .. 1 heart of health

-The expected health for a zombie falling off 24 blocks is 1/2 heart, but the zombie dies.
-zombies die when falling from height in 23 blocks (must have 2 unit of health)
-zombies have 2 units of health after falling from height in 22 blocks (must 3 units)
-zombies have 11 units of health after falling from height in 13 blocks (must 12 units)

Version Minecraft: 1.5 Pre-release