Sponges aren't working, when I place them, people can build and destroy.

I placed this sponge - as shown, and my friend could break it.

 

I believe this is to do with the plugin, it has happened to quite a few people.

 

I found a base and was also able to break the sponge

 

my bases sponges have been tnt'ed no matter how i arrange them. makes me kinda want to find a place with slightly better managed games to play.