Sulfur cube with TNT inside has some explosion drop decay, even with tntExplosionDropDecay false

The Bug:

Sulfur cube with TNT inside has some explosion drop decay, even with tntExplosionDropDecay false.

Steps to repro:

1. Turn off tnt explosion drop decay

2. spawn sulfur cube on flat land

3. give the sulfur cube tnt

4. explode the tnt inside the sulfur cube.

Expected Result:
All blocks exploded drop

Observed Result:

Only some of them drop.