I have tried spawning various Mk2 coaches in free roam and coupling to them, but it won't work. If I spawn the Flying Scotsman and a Mk2 railtour coach for example, and set both couplers to buckeye, they just bounce off each other. If they are set to hook, the coupling prompt does not appear. The buckeye coupler appears to not work with any other rolling stock, the hook works with some. For example a class 08 was able to couple to it. Edit: Also happening with some Mk1 coaches