Deallocate error on pointer obtained through C_F_POINTER

Hi, 

I am facing an issue with ifort 17.0 (the same code was working fine with ifort 12.1 and 16.0) on a simple code where I try to deallocate the fptr returned by C_F_POINTER from ISO_C_BINDING (I associate there the pointer to a C allocated array of char). The error on program compiled with ifort 17.0 is:
forrtl: severe (173): A pointer passed to DEALLOCATE points to an object that cannot be deallocated

Here is the snippet of code:

program testalloc
  use ISO_C_BINDING
  implicit none

  interface
     function c_alloc(buf) bind(C,name="alloc_in_c")
       use ISO_C_BINDING
       integer(C_INT) :: c_alloc
       type(C_PTR), intent(out) :: buf
     end function c_alloc
  end interface

  type(C_PTR) :: cptr
  character, dimension(:), pointer :: fptr
  character(128) :: s
  integer :: len, i

  len = c_alloc(cptr)
  call C_F_POINTER(cptr, fptr, (/len/))

  s = ''
  do i=1,len
     s(i:i) = fptr(i)
  end do

  print *,"obtained string = ",TRIM(s)

  if (associated(fptr)) then
     deallocate(fptr)
  end if

end program testalloc

As no error was detected with previous version of the compiler, I was wondering if it could be a bug in this 17.0 version or if my code was simply not valid but that was not detected/enforced previously?

Thanks
Olivier