The visitor mode prevents players from mob interaction, which means that the player would not be able to punch mobs or cause damage via mobs. However, even when the player cannot attack anything, he/she can still use mobs to destroy blocks.

Players can use explosive mobs to grief the progress of other players. For example, one can bait a ghast to destroy portals or lure a creeper to destroy another person's base. Even though this sounds intended, it is not the purpose of visitor mode so it has to be a bug.

It is expected that all explosive mobs should ignore players in visitor mode, or custom modes with mob interaction off to avoid griefing.

Steps to Reproduce

1. Spawn some creepers at least 20 blocks away in creative and operator mode

2. Switch to survival and visitor mode

3. Walk up to the creepers, and let them explode

Expected Results

The creepers should simply ignore you. 

Actual Results

The creepers explode and destroy blocks, bringing unwelcome damage to the world. (That should not be a part of visitor mode!)