Adding water or powdered snow to the cauldron will not extinguish the fire arrow

I used a bow with fire arrows to shoot arrows into the cauldron, and then poured a bucket of water. The arrows were still burning and the water is still full.But if there was already water inside, the fire will be extinguished and the water level will drop by one grid.

Expected Result..：‎
Pour water, the fire on the arrow will be extinguished and the water level will drop by one grid.

Observed Result...：‎
The fire was not extinguished and the water was still full.

Reproduce：‎
‎1.Prepare a cauldron, a bow with fire arrow and a bucket of water.

2.Put the cauldron down and shoot an arrow into it.

3.Pour water into it.Then you will find that the fire was not extinguished and the water was still full.