Interesting. I get similar results with this approach using room boundaries instead of model lines. I suspected it had something to do with the room bounding nature of walls but if it’s happening with Model Lines too then something else may be going on.
In your example it’s the elevation in the Y axis. In mine it’s in the X axis.wonder if there’s something in there too.
Jeremy, if you haven’t seen my post on the issue you might check it out here – http://dynamobim.org/forums/topic/elevations-by-room/