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.