The bug

When a creeper is given a higher ExplosionRadius tag and mobGriefing is false the creeper has the normal ExplosionRadius of 3, but when mobGriefing is true the ExplosionRadius is as it is set to.

The first image is with mobGriefing set to true and the second is with mobGriefing set to false

How to reproduce

1. Set gamerule mobGriefing to false
2. Execute this command:

   /summon minecraft:creeper ~ ~ ~ {ExplosionRadius:10}

3. Ignite the Creeper
4. Do the above again, but with mobGriefing set to true
   → Observe how the creeper explosion radius doesn't work with gamerule mobGriefing set to false