Finally, there is a temporary solution for the railroad bug!

[Gojira54]

Actually this thread was started this month.

I think if you have citizens that are unhappy and from another culture you get this bug. That would explain why it eventually goes away, at different rates for different cites, and when the war ends.

Just a guess, though, since I have never noticed it before.

 

[Doc Tsiolkovski]

The city gets connected once you learn the next tech. This is my preferred era for war (mostly since I fight to get that Coal ), I've seen it often enough.
Dunno why learning a new tech has such an effect, but it also autopicks the temporary unit when building an obsolete UU (like you still build Hwachas in Industrial 'cause you had no GA before).