Not aware if the tall grass lighting infinite fire is a bug, if it is, so this is NOT a duplicate, but certainly related!
If you put out the fire with, say, DIRT. The fire is STILL THERE, it even still generates light, and the worse: if you then remove the dirt block you just put, yes, you guessed it, the fire is back. It's as if the fire is on the block ABOVE the tall grass, so there is no use destroying/replacing the tall grass, you have to fill the block ON TOP of it to really extinguish the fire (thus, you have to put a block to replace the grass, then one on top of it, to do the job, since you can't really put the block on top of tall grass)
Now, on a related not, I hope the infinite tall grass fire is a bug, because that's very weird to have a lot of fire in heavy rain.