Orientation of rails aren't saved in structures

Cloning rails with /structure save and /structure load does not preserve their orientation.

Steps to reproduce:

1. Open the attached world rails-in-saved-structures.mcworld .
2. Flick the lever. It saves rails in a structure, and loads it at a different location.

Expected result:
The orientation of rails are preserved in the copy.

Observed result:
The orientation of rails are not preserved in the copy. Rails are placed in the world as if they were generated with /fill.