It's not visual bug. I fell from 4 blocks and hp went to 18% went back to 19% I set it to peaceful health went to full and set it back to normal difficulty and fell from 4 blocks again but health regenerated to full. If you take more damage than 19% it will not regenerate back to 20% like normal if difficulty is easy or higher. It's still effecting new worlds too I found out. If you take more damage than more than 1/2 on 9th heart. It's very annoying looks like some of us will be hanging out in creative for awhile.