Sorry to hear you are facing that issue. It hasn't been reported before but I can reproduce it here. Unlike V-Ray CPU, for V-Ray GPU the integration of RailClone is handled by Chaos so we'll have to discuss it with them. It may also be worth reporting on their forums.
In the meantime the only workarounds I can find are to either change the Proxy Display mode to Full Mesh or to instantiate the RailClone object using RailClone Tools.