That is the expected behaviour because Segment->Mapping is designed to generate a continuous mapping along the RC path (or X/Y directions for arrays). We can say that UV coordinates are local to the RC object, although not exactly because it follow the path.
If you need local UV coordinates to the segment, just apply a standard UVW modifier and uncheck Segment->Mapping. RailClone will use that mapping, and also can be modified using a UVW XForm operator.