File "pr7402.ml", line 1:
Warning 63 [erroneous-printed-signature]: The printed interface differs from
  the inferred interface. The inferred interface contained items which could
  not be printed properly due to name collisions between identifiers.
  File "pr7402.ml", lines 14-16, characters 0-5:
  Definition of module M
File "pr7402.ml", lines 8-11, characters 0-3:
  Definition of module M/2
  Beware that this warning is purely informational and will not catch all
  instances of erroneous printed interface.
module M : sig type t val v : t end
module F : sig module M : sig val v : M.t end val v : M/2.t end