Found at http://groups.google.com/group/comp.lang.fortran/browse_thread/thread/1abc1549a6a164f1/
by James Van Buskirk:
-------------------------
module M1
   real x
end module M1

module M2
   contains
      subroutine y
      end subroutine y
end module M2

module M3
   use M2, x => y
end module M3

module M4
   use M1
   use M3
end module M4

module M5
   use M4
end module M5

module M6
   use M5
end module M6

program test
   use M6
   interface
      function x(z)
      end function x
   end interface

   write(*,*) 'Hello, world!'
end program test

function x(z)
   x = z
end function x
-------------------------

g95:
In file a.f90:31
      function x(z)
                1
Error: Name 'x' at (1) is an ambiguous reference to 'x' from module 'm1'

NAG f95:
Error: a.f90, line 31: Symbol X resolves to X in module M1 and to Y in module M2
       detected at FUNCTION@X
Error: a.f90, line 31: Redeclaration of symbol Y from USEd module
       detected at FUNCTION@X
Error: a.f90, line 31: Duplicate subprogram name Y
       detected at FUNCTION@X

valgrind:
==7549== Conditional jump or move depends on uninitialised value(s)
==7549==    at 0x416222: get_proc_name (decl.c:712)
==7549==    by 0x4186DA: gfc_match_function_decl (decl.c:4054)
==7549==    by 0x44EE4F: decode_statement (parse.c:116)
==7549==    by 0x44FAE4: next_statement (parse.c:505)
==7549==    by 0x451023: parse_spec (parse.c:1747)
==7549==    by 0x4527B5: parse_progunit (parse.c:2965)
==7549==    by 0x452C79: gfc_parse_file (parse.c:3271)
==7549==    by 0x479C24: gfc_be_parse_file (f95-lang.c:258)
==7549==    by 0x6D4B61: toplev_main (toplev.c:1039)