SaC fails to compile a constant with-loop from demos

Here is a SaC program:

int sel (int[.] iv, int[*] a) { return _sel_VxA_ (iv, a); }

int main ()
{
  a = with { 
            ([1,1] <= idx <= [7,10] step [3,2]): 3;
      }: genarray ([9,12], 0);
  return a[[0,1]];
}

Here is the error message:

Internal compiler error
Assertion "!WLGRID_ISMODIFIED (grid1)" failed at /tmp/sac2c/src/libsac2c/wltransform/wltransform.c:5036 -- grid was modified
Please file a bug at: http://bugs.sac-home.org

The version of the compiler is:

sac2c 1.2-beta-BlackForest-611-g777dc
build-type: RELEASE
built-by: "tema" at 2017-11-21T12:36:57

Commit #777dcd63

Any ideas?