On Steams Stranded Deep version 0.90.00 the container shelves are floating. I tried putting the shelves on while on sea and land. I was unable to put them on the raft. The outline would turn white for placement higher up. I quit then went back into the game to try again but with the same results. The first time I have seen this was while watching GranddaddyGamer’s YouTube channel.
They snap in place on the raft, but they’re in the air. If you place them, then they will stay fixed to the raft, but will be a little higher than normal.