Sea Pickles will act normally if you place them in a water source block. If you place them in running water or underwater in a non source block of water it changes the water to air. If it's one block deep the water just disappears. If you are underwater it creates an air block as big as the pickles.

seed: -8300275442758179407 (superflat)

Edit: This is probably related to turtle eggs and pickles blocking lava and water from flowing (MC-128001).