I was placing glow lichen around a cave, when I encountered a water source. I then placed glow lichen on the floor of the cave, and discovered that water would flow on top of glow lichen without breaking it. After this, I then tried swimming in the water. I started bouncing up and down rapidly. This is a fairly easy bug to reproduce. Just place some glow lichen under water:

Then move into the water, and start sprinting/swimming. You will bounce up and down incredibly rapidly, as you swim, shrink down to one block, have no water in you, as you're now in the glow lichen, and then go two blocks tall again, only to continue to swim, shrink, stop, and enlargen. I don't think this is intentional, but it may not be a bug.