Sea lanterns surrounded by clay only illuminate one side

Sea lanterns as shown in the screenshots on their own (see track) illuminate all around.
Those surrounded by clay (see signs) only illuminate on the south side, not north. Unsure if this has been replicated east and west, up and down, or with other materials. If I were to face south and place a block of any sort (probably causing a block update) they begin to light.
Reproduction is as you see in the image.