This is truly the strangest bug I have ever seen. While trying to get footage for MC-227154, I found something much weirder. Just see for yourself.

To reproduce

1. Summon a blaze (blaze A) with whatever UUID you can randomly type. For example:

   /summon minecraft:blaze ~ ~ ~ {UUID:[I;1,2,3,4]}

2. Optionally, you can put blaze A into an enclosure
3. Spawn another blaze (blaze B)

   /summon minecraft:blaze

4. Summon a snowball with an Owner tag that matches the first blaze's UUID. Make sure it hits the second blaze.

   /summon minecraft:snowball ~ ~ ~ {Owner:[I;1,2,3,4]}

   → Blaze A starts to take damage and then dies, even though no actual fight takes place.

Video

2021-06-06 12-07-37_Trim.mp4