I know that this bug is in 1.8 or 1.8.1 because of the timestamp if the video and because they say in episode 1 that it's 1.8, but I had to say that the bug is in 1.8.7 because the bug tracker won't let me do past versions.
https://youtu.be/VhJpxHxHJ_8 at ~8:23
The summary & the video explain it all, even though it happened in 1.8 or 1.8.1, I have looked through the bug fixes that have been made since then, and none of them are about lava. I have also searched the bug tracker, but I can't find a ticket like this one in PC Minecraft. However, there is a related, if not identical, issue in Pocket Edition, MCPE-8166. Someone should test this to see if it occurs in the latest version.