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.