End crystals heal dragon after being destroyed

Upon fighting the ender dragon, when attacked, the ender crystals explode and the fire animation stops, but the crystals remain and still heal the dragon.

I can't seem to be able to reproduce as, when recreating the same environment (Superflat, Void preset, /setblock ~ ~ ~1 end_portal, then destruction of a crystal with a snowball), the bug doesn't reappear. Furthermore, the previously broken crystals disappear upon re-entering the world.