Podzol doesn't convert to dirt when blocks are above it

The Bug:

Podzol doesn't convert to dirt when blocks are above it.

Blocks such as grass blocks and mycelium convert to dirt when blocks are placed above them, but this same behavior cannot be seen with podzol which is strange since podzol is very similar to grass blocks and mycelium.

Steps to Reproduce:

1. Place down some podzol and then place another block on top of it.

2. Wait for around one minute and see if the podzol converts to dirt.

Observed Behavior:

Podzol doesn't convert to dirt.

Expected Behavior:

Podzol would convert to dirt.