Thanks for reporting this issue, I can reproduce it here.
Unfortunately V-Ray RT does not have an SDK and the RailClone implementation was handled by Chaos Group using our API. I have emailed them about this problem and hopefully it can be resolved in a future release. In the meantime, if you set the Proxy Object's Display setting to Show Whole Mesh it should render fine. If you want to cut down on the number of polygons being displayed in the viewports you can still select the V-Ray Proxies, right click and select Object Properties and then turn on Display as Box.
I hope that helps.