Charged and normal Creepers in boats do only 1 damage to nearby entities when exploding

The bug

This bug was discovered when trying to get a creeper head by exploding a charged creeper beside a creeper. Both creepers were in boats, the charged creeper blew up leaving the other creeper right beside it relatively unharmed. Very distressing.

Also tested two ordinary creepers with same result, and an ordinary creeper beside a player who took just half a heart of damage. The boats also do not take damage, however may be thrown into the air and break on landing.

However, maneuvering the boats to sit on the edge of a block, ensuring the creepers' feet are hanging in air, blowing up one of the creepers will kill the second creeper and both boats. It seems that as the mob is technically hanging slightly below the top of the block, their explosion damage on nearby entities is drastically reduced.