When the fake curved rails are flipped nothing happens. If they are in blueprint then their coordinates flip, but some of the images don't flip.

Because there are no vanilla entities with 8-way rotation without side effects, I was not able to get flipping working. You might notice that when you manually rotate a curve you only get half of the possible orientations for that curve (the four that curve the same direction).

Finding an entity that can handle 8-way rotation could fix this. The alternative would be a custom flip handler, which I wasn't able to figure out. I'm open to a PR either way!

1.1 curved rail has rotation and flipping (when in a blueprint at least. I don't know how to select it otherwise), so 8 orientations, can't you combine/link the mod's curved rail pieces in the same way, so that they have 4-way rotation + flipping? So instead of having one piece that can be rotated in 8 directions and flipped, for 16-orientations, have two pieces that both have 4 rotations and flipping. I think the entities that are numbered with 1 and 2 should be paired in this case.

Flipping in blueprint does work for the ramp, and kind of for the elevated diagonal-to-half-diagonal and normal orthogonal-to-half-diagonal, but those are actually rotated twice instead, so it doesn't always work. For the other pieces nothing happens (if I checked all).
Edit: I think that the 180 degree rotation happens with all entities, but is only apparent with the curved rails, as those are asymmetrical.

The vanilla rail entities are very specialized. I was not able to find a way to repurpose them.

The train remnant and cargo wagon remnant can both be rotated in 8 directions as well.