User blog comment:TienShenLong/Why Pure Habitat does not stack on storage?/@comment-10760902-20130929073138

Different ID, I suppose, Before the L&W update, there are Pure Terra Habitat, Pure Flame Habitat...etc. So the old ids must be different. After L&W update, all existent Pure Habitat "transformed" to one single Pure Habitat. So that proved that SP has change all properties of the Old Pure Habitats into same new properties. But ID can't be changed of course, so that's why they are not stacked together since their IDs are not the same.