Rounding error on fall damage

There's a rounding error when falling from a height of 12 blocks. 

Starting with falling from a height of 4 blocks, the player takes half a heart of damage, and the damage increases with 0,5 per extra block of falling. 

This works up untill falling from 12 blocks height, witch should do 4,5 hearts damage. But instead, it does only 4.