Server and single player crash dispensing fire downwards to the side of obsidian

I'm reporting this as private since I don't want to add any further fuel to the fire. However, a reddit user (not me) has already publicised it far and wide on multiple subreddits.

For example: (Video of my previous post) HUGE BUG! "Server crasher" (And singleplayer) Current version (Java 1.16.4)

I just confirmed the crash in the latest 1.17 snapshot (20w51a), and commenters on the reddit post have confirmed it affects the 1.16.4 release.