Foxes sleep on top of honey blocks, even in broad daylight

Same happens with soul sand.

I attached a video if that helps.

Well, Is that a bug or a feature, because if it was a feature it would be cool.

Does this also affect farmland, grass paths and fully stacked snow layers?

Farmland, grass paths and fully stacked snow layers are not affected. As for soul sand, I could not reproduce, meaning that honey blocks are the only blocks that makes foxes go to sleep.

Even if the fox is a baby, it won't sleep on farmland, grass paths, soul sand and fully stacked snow layers but will sleep on honey blocks.

And no, they don't sleep if their are inside a cauldron.