When Strecthes (SMB3) are placed underwater, normal Stretches and upside-down Stretches move correctly before they disappear for the first time. However, when they reappear, they now float in the air, and never return to the blocks they're supposed to be stationed at. I have them and the blocks on a layer separate from default, and the Filter Layers box checked as recommended.
Similarly, when I have the Filter Layers box unchecked, they float anywhere on the X-axis, even moving through walls, and can sometimes move on the ceiling and floor instead of their designated platforms. I've embedded a GIF showcasing this bug.