I'm very embarrassed to say this. Those code examples weren't non-compiling OCaml, but valid SML. Once I remembered the existence of the language (in my defence it was never mentioned in the thread), I managed to compile the code, and confirm my suspicion:

`val point: Bound.shape = Shape.Point` type-checks, because `type shape = S.shape`. To drive the point home, so does

    val DoesNotReturnPoint : Shape.shape -> Bound.shape = fn x => x