I didn't think of E18 being routed on the ramps to the east, since the point there seemed like it was on the motorway on the high bridge and not in the roundabout there. What signs/official mapping did you find? I looked at several maps (Statens vegvesen, OSM, Michelin, Google, Bing, Mapquest, Yahoo, Yandex, Visit Norway, Here WeGo) and each indicated that E18 is on the high bridge. I also found
http://www.vegvesen.no/_attachment/688111/binary/1014145?fast_title=Planbeskrivelse+E39+Gartnerl%C3%B8kka%E2%80%93Meieriet+%28NB%21+23+MB%29.pdf which is a planning document for the replacement of the roads in the area to make it better for traffic flow into the future. On page 20, it talks about how E18 comes out of the tunnel and crosses the high bridge, while local traffic takes the ramps. This routing is also confirmed on page 23. On page 25, it talks about how in the fall of 2013 the high bridge was made into 2 lanes eastbound and one westbound and no shoulders. It says that E18 went down the ramps prior to this modification of the lanes, so that must be when it was moved to not go to the roundabout to meet E39. I know this is just a planning document in the early phases of what they want to do for improving and replacing the roads, but the little bit of what has been done so far to try to relieve the congestion and the current description of the routes seems to indicate that the old routing is what is in the highway browser now. I know this is just for the public discussion phase of the planning, so it will be a while before they do construction and routes will change along the way. I didn't go through and have Google translate all 106 pages, since my knowledge of Norwegian is non-existent, so there could easily be more relevant information about the routes in question that I did miss.