Hey there!

I recently encountered a bug concerning fire mechanics. This only occurs when the "fire spreads" setting is turned off. 

When the block below a fire is broken, the fire doesnt extinguish and becomes almost "invincible". It becomes eternally lit and impossible to extinguish by hitting it and using splash bottles (It can be extinguished by placing a block on it, using flowing water or blowing it up). The fire also still performs most of its normal mechanics such as lighting things on fire and emitting light.

This occurs both on creative mode and survival mode and the fire reappears normally again when a block is placed underneath it. I also found out that the "invincible" fire will still exist even after the "fire spreads" setting is turned off.

Heres a link to a video I shot showcasing the whole thing:

https://youtu.be/ubwRq8XSAqM