The Summary:-

Podzol doesn't not spread when four spruce sapling are bone mealed.

How To Reproduce:-

Step 1:- Take four spruce saplings.

Step 2:- Place four spruce sapling in grass blocks.

Step 3:- Bone meal the sapling till the tree grows.

Observed Results:-

Podzol doesn't spread to the grass.

Expected Results:-

Podzol should spread after when the tree is grown.