I bred 2 horses twice and created 2 foals. I fed both wheat until they were fully grown.
Both the new horses have 12 hearts but only 8 1/2 hearts are filled. They do not heal the rest over time (near hay or while riding). I injured one once by jumping off a roof, but it only healed back to 8 1/2 hearts.
Edit: After a little more play time the horses now have only 8 hearts with no extra unfilled hearts.
Seth Williams
I also have this issue on 1.14.1.
I bred 2 horses twice and created 2 foals. I fed both wheat until they were fully grown.
Both the new horses have 12 hearts but only 8 1/2 hearts are filled. They do not heal the rest over time (near hay or while riding). I injured one once by jumping off a roof, but it only healed back to 8 1/2 hearts.
Edit: After a little more play time the horses now have only 8 hearts with no extra unfilled hearts.