Wither blue skulls can destroy light blocks

The blue skulls shot by withers can destroy light blocks. As blocks with similar blast resistances (e.g. bedrock, command block, and barrier) are indestructible, this may be a bug.

Steps to reproduce:

1. Create a superflat world with light blocks on top.

2. Summon a wither. Wait for it to attack some entities with blue skulls.

3. Hold a light block while in creative mode in order for particles to show. The light blocks are no longer present in the impact crater of the blue skulls.