I don't know whether this is a bug or intentional (in the latter case, it would mean yet another culled feature), but moving background objects do not move in the editor. In fact, it isn't even possible to enter a direction of movement for them.
Inside the player, it works for a level from SEB Lems I tried out - Mother O'Donoghue - but not for my converted Autumn tileset level (the leaves remain static in the air).
I know that triggered decorations have been removed in New Formats, but moving background objects are a different category.
I also mentioned this in my graphic sets thread, but I think it gets lost there easily, so I bring it up here again.