To reproduce, light youself on fire then immediately put it out, and you won't catch on fire. Do the same to mobs, and they will catch on fire, regardless of how short they were in fire.
Linked issues
is duplicated by 1
Comments 5
This is most likely intentional behavior, as Mojang has fixed MC-295690 in 25w19a.
Can confirm. The player has to take damage from fire, at least 3 times in order to remain being damaged whilst stood outside of fire. This behavior is inconsistent with mobs.