Ifort accepts invalid code

The code below discussed in an interp is accepted by ifort (as it is by nagfor and gfortran, but rejected by PGI fortran). According to J3, the code

is invalid: https://j3-fortran.org/doc/year/11/11-219r1.txt

I am not sure whether the compiler actually has to catch this as the standard uses 'shall', but I opened a support request to clarify with  the intel team. Here is the code:

       MODULE M1
         INTERFACE SUBR
           MODULE PROCEDURE SUBR1
         END INTERFACE
       CONTAINS
         SUBROUTINE SUBR1
         END SUBROUTINE
       END

       MODULE M2
         INTERFACE SUBR
           MODULE PROCEDURE SUBR2
         END INTERFACE
       CONTAINS
         SUBROUTINE SUBR2
         END SUBROUTINE
       END

       PROGRAM MAIN
         USE M1
         CALL S
       CONTAINS
         SUBROUTINE S
           USE M2
           CALL SUBR
         END SUBROUTINE
       END