When placing a glass pane as a window in a house (or any other time) underwater, the water stays as normal (occupying all of the air in the pane). When I use a sponge or water bucket to get rid of the water one side (in the part of my house filled with air), the water disappears both sides (so an air pocket on the water side in the glass pane). When I put the water back in the air pocket, it flows through the glass again. Also happens with iron bars, fences, trapdoors, doors and cobble walls. It makes no sense that the water does this and it looks incredibly wierd, as if water is flowing through solid glass.