I'm curious as to when copyright issues might arise in manufacturing components that are compatible with major brands. For instance, would making a stem that's designed to fit Dahon's integrated headset design breach copyright, or would that only apply to a complete bicycle design that clearly appropriates those specific design attributes?

Similarly, despite Brompton patents having expired it appears there's still some claim there to intellectual property rights with regards to the overall design. Would e.g. a third party fork designed specifically to fit the brompton breach any copyright? Or a rear frame?