Minecraft wiki entry for Development_versions, associated text: MC-3524 – Structure related mobs do not spawn in flat type world generation.
MC-146854 – Player movement favors x axis when in a corner.
MC-156309 – TNT entities don't properly collide with blocks when being fired in X direction.
MC-165974 – Game pushes east/west when jumping from the inside corner.
MC-179315 – Ruined portals never generate in Superflat worlds by default.
MC-187911 – minecraft:endcity structure has no underscore while end_city_treasure does.
MC-197128 – If a custom biome uses multiple configured structure features of the same type, only one of them can generate.
MC-210612 – Strongholds do not generate in certain customized worlds despite /locate saying otherwise.