This was also kind of displayed in an IbxToycat video on YouTube (This 1.18 feature can RUIN your world (or save it) )
with their existing world.
I should have also mentioned that my world was also an existing world already, but that may have been guessable.
Possible duplicate of MC-2497?
Ali describes it better IMO. I'm seeing flames jumping all over the screen. It's so distracting that I've abandoned playing for now, hopefully it will be soon fixed. I've only played with released versions, so if 1.4.3 was never released, that may not be the version the OP intended.
Linux astaroth 3.6.6-1-ARCH #1 SMP PREEMPT Mon Nov 5 11:57:22 CET 2012 x86_64 GNU/Linux
I have lost access to this world, so I no longer know if it affects worlds with both 1.17 generation and 1.18 generation. However, I have since created a new world in 1.18, and haven't noticed the issue.