Bubble columns can be blown up with TNT

This one is debatable (if it should be fixed, or left as is to "nerf" such defenses) but making note of this. I'm pretty sure this is a side-effect of patching waterlogged blocks so they can be blown up. You can blow up bubble columns with TNT. This means that bubble column defenses are largely ineffective (in fact, they are less effective than standard water walls, as you don't need a hybrid (TNT+sand/concrete) shot to get through)