Joining tracks is a bit broken. Appears to be at junctions. They don’t join yet you get charged anyway.
I think it’s all to do with directions and such of junctions, if you have 2 junctions close together, it won’t work. I don’t think it’s a “bug” more of a “feature”.
Plus, although it says you get charged, I don’t think you actually do.
As mattz0r said I don’t think it’s a bug so much as a feature of the game, although I could be wrong…
I’ve wondered about the getting charged too but I don’t think you do, the little bubble is thee but it doesn’t. That’s probably a bug to report though
But it works if you delete the junctions and recreate them.
If you go to 7 seconds in (youtu.be/nLPZlohdzi4?t=7)
You will see that the lower one is going in one direction, the upper is going in another direction (the yellow and black arrows indicate this.
This means that the two won’t fit together, because they are going in different directions.