Podzol does not change into dirt when sapling grows into tree

In a world created on 14w33c I switched into creative mode and selected podzol some saplings and the bone.

I placed the podzol down and placed various saplings on top of it. I used the bone meal to grow the saplings into trees.

When i did so, the podzol did not change to dirt.

Isn't it supposed to change to dirt when a tree grows on it?, the wiki says so