When you're riding the boat you can mine blocks that are under the boat which is a bug
How to reproduce
Craft a boat,
Ride the boat and you can start mining under the boat.
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Comments


This behavior isn't considered a bug. There's no reason why you shouldn't be able to mine blocks while riding a boat. The entity you're riding is consistently untargetable, allowing you to interact with blocks or entities by aiming through it.

This behavior isn't considered a bug. There's no reason why you shouldn't be able to mine blocks while riding a boat. The entity you're riding is consistently untargetable, allowing you to interact with blocks or entities by aiming through it.

Dolphins you've got a good point, but how does it make sense that you can mine blocks under a boat and can also break the boat?

This should be WAI per MC-19163.