Obby damaged when covered in water

Your username:
Jovan
In which minigame/server does the bug occur:
Factions
Detailed description of bug:

So fearzz used a cannon to raid our base last map
apparently how he did it is, when obby explode in MIDAIR the obby gets damaged
fix it.
As far as I understand this is how he done it.
heres a picture example

 

This is not a bug. When TNT explodes a block above the water, it takes damage. This does NOT happen with cobblestone, though. If your main base is made from obsidian, I suggest putting multiple reverse layers on top and on the bottom of your base.

 

I am grateful for your reply, but any of you who doesnt play factions, dont reply please.