In the attached image, you can see Hedeby has a railroad connection with Cordoba (that has the railroad trade icon correctly displayed, because it has a harbor that connect it with Madrid, the capital, in another continent) and has the road trade icon.
I've made several tests and the reason Hedeby doesn't have the railroad trade icon is because it's a puppet, without harbor, on another continent. Owned cities (not puppets) without harbor, connected by railroad to a harbor city correctly have the proper icon. Same with puppet cities that own a harbor.
I've made several tests and the reason Hedeby doesn't have the railroad trade icon is because it's a puppet, without harbor, on another continent. Owned cities (not puppets) without harbor, connected by railroad to a harbor city correctly have the proper icon. Same with puppet cities that own a harbor.