Blocking with a shield negates the damage of a blaze fireball impact but the player is still set on fire.

I was fighting blazes when I decided to block their fireballs with my shield but, I was set on fire. I tested it in a creative world by equipping a shield, turning my gamemode to survival, and summoning a blaze. I got  the same result; I heard the shield blocking sound, I didn't take damage from the impact but, was set on fire. I searched for similar issues but, found none.