The roof of dungeons are overridden whatever block would have spawned there if the dungeon wasn't there while the rest of the dungeon (walls and floor) remain as cobblestone and mossy cobble. I was able to see the same thing happen with multiple dungeons. Cave features were also able to generate in the dungeon like the glow lichen pictured in the 3rd image.
seed: 5937531705580132167
Coordinates: (1008, -40, -310), (1120, -25, -350), (1195, 22, -256)
Dungeons have never had ceilings