End-Game Mecha 0 Sion Bug

This bug is truly horrible. It destroys the end-game potential of Sion when using the Mecha 0 skin. The bug is this:

If you ult right as the nexus is exploding, or if you are already ulted, you will not turn into a train/no longer be a train. Instead, you will just be in humanoid robot form. Please fix. How is the pain train supposed to end games if he can't be a train. HOW.