Mobs summoned already burning start taking fire damage only after a second

If you use the command to spawn a mob (let it be a Creaking) that is already burning and the value of «Fire» is 19, then the Creaking will not die from the fire and will go out. However, if you specify the value of 20, it is exactly one second, then it will immediately die. Reproduce:

• Use command: /summon creaking ~ ~ ~ {Fire:19}

It will not die from the fire and will go out.

• Use command: /summon creaking ~ ~ ~ {Fire:20}

He will immediately die from the fire.

It seems that this behavior can be justified by the fact that when a mob starts burning, it cannot start to burn immediately, but only after a second (this is just 20 game ticks).