Some invulnerable entities will appear to be on fire indefinitely until you unload the chunk they are in or reload the world.

Affected Entities:

• End Crystal ^{_{In 1.21-pre2 and above, end crystals do not catch on fire}}
• Painting
• Item Frame (with and without an item in it - Note: In 20w17a and above, the flame animation might not appear, but the Fire NBT tag is 100s)
• Glow Item Frame (with and without an item in it - Note: In 20w17a and above, the flame animation might not appear, but the Fire NBT tag is 100s)
• Lead / Leash Knot
• Minecart

Steps to Reproduce:

1. Give yourself a bow with Flame and some arrows

   /give @s minecraft:bow[minecraft:enchantments={levels:{"minecraft:flame":1}}]

2. Summon one of the affected entities above is the invulnerable NBT tag
3. Shoot the entity that you have summoned

Observed Results:
The entity will be on fire indefinitely.

Expected Results:
Either they do not catch on fire or the Fire NBT tag extinguishes the entities properly.

Notes:
Code analysis by marcono1234 can be found in this comment.