I can see where this would be useful if you have another line stopping at the same station that you want to transport those goods. The problem in TF is that, unlike TTD, the player currently does not control how cargo is routed. As a player you’re just making lines available and letting the AI determine how they are used.
In your case the AI has determined that loading up those goods is a more attractive option than whatever else you wanted to happen. The fact that there’s only one car type for multiple goods also doesn’t help as you can’t even use the consist to define what should be carried.
This seems to be the design philosophy underlying the game, so I don’t know if it’s going to change. The only thing you can currently do is make another station and route somehow more attractive to the AI for the goods.
In my current game I am trying to use just steel mills. I *think* it should be the most profitable since it takes 2 types of raw mats. As a bonus there’s no goods car attached so I take it where I want. :p
@ben, you basically get a free train if you line up the two raw materials in series because for some reason a car can take both x tons of coal and x tons of iron ore at the same time (rather than one or the other as it should logically be). I think that should be fixed so that it can only be loaded up with one type of good at a time.