there was a lot of that when i was recreating my house's interior in maya... i created most of it with nurbs and found that the viewport shaded view was different than the rendered view... i basically just ignored what the shaded view was telling me and went what i got from the render. any hardware view can differ from an actual render view, so a test render helps. trust what the render shows you as opposed to the viewport. it may be a simple graphics driver issue, but if you can still correct the error and have it render correctly, who cares what the viewport tells you?