Passive mobs can spawn in campfires and soul campfires

Animal mobs can spawn on campfires and soul campfires that have a grass block below them, provided normal spawn conditions for them are met. It doesn't matter whether the campfires are burning. This can be exploited to make fully automatic farms that produce cooked food in large quantities, as in this farm by SlackLizard: https://www.youtube.com/watch?v=PI7fRCKhnoU.

Steps to Reproduce:

1. Open the attached world Spawn on campfires.mcworld.
2. Look down at the spawning platform covered with campfires.
3. Wait for messages in chat.

Observed Results:
From time to time you can see an animal spawn on the campfires and (if the command block lever is enabled) command output tells you where it spawned. It is then killed (to avoid repeating the output messages).

Expected Results:
Nothing should be able to spawn on fire from a campfire or soul campfire.