The Bug

Advancement criteria for killing a brown rabbit (RabbitType:0) can be falsely triggered by killing any entity, but only if the advancement has multiple criteria.

How to Reproduce

Download the attached datapack. There are a lot of advancements for testing various bugs, but we're just using the ones named Brown Rabbit and Two Rabbits.

The Brown Rabbit advancement has one criterion, for killing a brown rabbit.

The Two Rabbits advancement has two criteria, one for killing a brown rabbit, and one for killing a white rabbit. Like so:

  "criteria": {
    "brown_rabbit": {
      "trigger": "minecraft:player_killed_entity",
      "conditions": {
        "parent": {
          "type": "minecraft:rabbit",
		  "nbt": "{RabbitType:0}"
        }
      }
    },
	"white_rabbit": {
      "trigger": "minecraft:player_killed_entity",
      "conditions": {
        "entity": {
          "type": "minecraft:rabbit",
		  "nbt": "{RabbitType:1}"
        }
      }
    }
  }

Spawn any entity that doesn't fit any of this criteria and kill it. The Two Rabbits advancement becomes filled halfway, and the Brown Rabbit advancement remains untriggered. Confirm that the Two Rabbits advancement thinks you killed a brown rabbit:

/say @s[advancements={paint:testing/two_rabbits={brown_rabbit=true}}]