I'm playing with specifying interfaces for packed modules. Afaik, when
compiling library lib, if there is a file lib.mli, compiler will check
whether library obeys the interface in lib.cmi and then use that as
the interface for the library, otherwise the interface will be
inferred.

This is what I have.
foo.ml:
type t = int
let x = 5

foo.mli:
type t
val x : t

g.mli:
module Foo : sig include module type of Foo end


and I compile the library G like this:
ocamlopt.opt -for-pack G -c foo.mli foo.ml
ocamlopt.opt -c g.mli
ocamlopt.opt -pack -o g.cmx foo.cmx

No problems, everything works.

Now I want to get fancy and I add std.ml, and change g.mli (code
included as packed.tar.gz)

std.ml:
module Foo = Foo

g.mli:
module Std : sig include module type of Std end

and compile similarly like before
ocamlopt.opt -for-pack G -c foo.mli foo.ml
ocamlopt.opt -for-pack G -c foo.cmx std.ml
ocamlopt.opt -c g.mli
ocamlopt.opt -pack -o g.cmx foo.cmx std.cmx

But now I get this helpful error message
File "g.cmx", line 1, characters 0-1:
Error: The implementation (obtained by packing)
       does not match the interface g.mli:
       Modules do not match:
         sig module Foo : sig type t = Foo.t val x : t end end
       is not included in
         sig module Foo : sig type t = Foo.t val x : t end end
       Modules do not match:
         sig type t = Foo.t val x : t end
       is not included in
         sig type t = Foo.t val x : t end
       Type declarations do not match:
         type t = Foo.t
       is not included in
         type t = Foo.t


Does anyone know what is going on here?

Thanks,
   Milan