createExplosion Bug?

Whenever I use the method createExplosion(), and it was triggered by the placing of Obsidian (which is indestructable by explosions), no other blocks around it are damaged. I'll give an example:

Code:

public void onBlockPlace(BlockPlaceEvent event) {
               
        Location loc = event.getBlock().getLocation();
       
        World world = event.getBlock().getWorld();
       
                  world.createExplosion(loc, 4.0F);
       
}

If getBlock() returns Obsidian, then no blocks are destroyed, even if the Obsidian is placed on dirt.

If getBlock() returns any other type (I.E. dirt etc.), then any blocks in that radius are destroyed.

I understand that the Obsidian itself won't be destroyed, but why aren't the blocks around it being damaged?

Bug?

 

if the expotion happens inside the obsidian block, the obsidian blocks it. its unwanted behavor, but technicaly not an bug, because no things are breaking the rules against the behavor of tnt explotions