This is a visual bug that I had found out about on one of my survival worlds, while mining underground in a strip mine.
It happened to be a very simple visual bug, but one that may affect map creators, if something was hidden in lava, or something alike.
The way I had done it, I had gone into F5, lowered my vision until a third of it was under lava, and the rest was above, and then maneuver my angle, until you were able to clearly see everything under the substance.
Duplicate of MC-3615.