This may actually be an issue with the game changing the source block that the kelp is in to a non-source block when the kelp is broken by a piston. I've noticed that when I manually break all the kelp to "reset" the farm, some of the water blocks will become air temporarily before reverting back to being a source block. Sometimes it takes multiple times of planting and breaking the kelp to have it not do this. Whatever the issue is, it is 100% breaking my automatic kelp farm that I spent hours building. And over a week without the bug even having been looked at is frustrating as well.
Aaron Parris
REALMS-2921
This may actually be an issue with the game changing the source block that the kelp is in to a non-source block when the kelp is broken by a piston. I've noticed that when I manually break all the kelp to "reset" the farm, some of the water blocks will become air temporarily before reverting back to being a source block. Sometimes it takes multiple times of planting and breaking the kelp to have it not do this. Whatever the issue is, it is 100% breaking my automatic kelp farm that I spent hours building. And over a week without the bug even having been looked at is frustrating as well.
That appears to be normal functionality. Those are all waterloggable items.