How to activate this bug:

1. Set fire on Netherrack with Flint & Steel.
2. Break and replace the Netherrack with other solid block(Full Block).
3. The fire will light up automatically, and you can repeat the step 1 & 2 without extinguish the fire.

*The fire seems like won't extinguish itself.

*The 'Fire Spread' setting is turned off.

*The fire won't light up it if the Netherrack is replaces by non-solid block.

*Not sure if the fire will turn into blue fire if the netherrack is replaced by soul sand / soul soil.