One time, I was experimenting with different size creeper explosions, but whenever I put in a high explosion radius, such as 500, blocks would not break. I kept experimenting, and soon found out that 127 was the biggest explosion that still allowed blocks to break. However, entities still were damaged. I speculate that it has something to do with game processing ad the 8-bit integer limit (128).

How to Replicate

1. Enter the command, "/summon creeper ~ ~ ~ {ExplosionRadius:500}". (Again, it doesn't have to be 500. Just at least 128.)
2. Get a flint & steel.
3. Light the creeper.
4. No blocks break!