Old world map edges disappearance

When creating an old world type. The edges of the world on the second opening of the game always seem to glitch. The glitch causes the mobs and certain placed items, ex: bed, to appear that they are floating in air. In some cases those items are colored as usual but somtimes become black and seem to vibrate. When this happens the empty space that use to have blocks to stand on are either unassailable or can be walked on bur still does not show.