Stefan Nagy
To the original reporter: It may seem strange but all highways (in openstreetmap pedestrian areas are also some kind of highways) are rendered in front of underground trainlines – while buildings are not. So it's no mapping error, it's a rendering issue. Personally, I think it's a good idea, because it can be very confusing, when you have complicated road junctions and then (for a lot of use cases) irrelevant subway trainlines crossing those. However, if you think it's no feature but a bug, please file a report here: https://github.com/gravitystorm/openstreetmap-carto/issues