The original air of waterloggable blocks is replaced by water if the structure is spawned in water

I am trying to spawn large ships in the ocean, using MCreator 2022.2. While the ship spawns properly for the most part, its slabs and stairs under the water level are filled up with water instead of air, which means the ship's hold has water flowing all over the place, even though I saved those blocks without any water nearby. I'd like to know if this issue can be fixed using Mcreator, without having to replace the slabs and stairs by something else.