Thanks for contacting us. In this case the object is displaying as boxes to improve viewport performance. This automatically happens when the RailClone object exceeds a specified face count, which is why adding the pole segment triggers it. You can change this behaviour in the Display rollout.
By default RailClone uses the "Adaptative" mode: If the face count is below the value specified full geometry is displayed. If the face count exceeds the value specified, bounding boxes are used. To see the full geometry in the viewports, switch the mode to Mesh. Whichever mode you choose, this a viewport effect only, and the render will use the full geometry as expected. You can find out more about these features in our documentation
I hope that helps, please let me know if you have further questions.