Did not see this anywhere but probably a known issue. Was happening on my personal server with 20 or so mods. Made sure it was only railcraft and reproduced it on a fresh install of forge with only railcraft installed. This is in single player creative mode.

I have windows 7 64 bit home premium by the way. This is what happened when I broke the track where it should bend and then replaced it.

Hmm....

Should be fixed in Forge 10.12.1.1065