The coupling restraints on these carriages are wrong; i.e. building one first or first/second class (which also have incorrect class definitions by default) will result in a consist that cannot be continued.
Thank you for the report - I believe that I have now fixed this. I should be grateful if you could re-test with to-morrow's nightly build.
What was not mentioned here but discussed on the server was that they also have the wrong passenger classes. First class coaches of this set are no different than the other classes and all use "low" class with the same comfort and capacity. I am guessing a copy and pasting error here, that or they never were updated for passenger classes.
Thank you for that - I have now fixed the first class carriage, too.