I think that because litterboxes are made with plastic, they tend to hold odors. Maybe a quick cleaning of the plastic and metal parts of the Littermaid?

Also, I'm not sure on the ventilation of the room your boxes are in, but I know that helps alot. We have four in our den, one in the living room and one in the bedroom and because those are more open areas (has windows) it doesn't stink. But Livvy has her own box in her walk-in closet and I have to air out that room, even with daily cleanings.