multi-operator WL fails on multi-threaded execution

When compiling the following code:

int scan (int[256,8] a) {

    row = with {} : genarray([8], 0);

    a2, m = with {
        ([0] <= iv < [256]) : (row, 42);
    } : (genarray([256], row), genarray([256], 0));

    //StdIO::print (m);

    return _sel_VxA_ ([255], m);
}


int main (){

    test_array = with {} : genarray([256,8], 1);
    sum = scan(test_array);

    return sum;
}

the vector m::int[256] should be a vector with 256 values 42. In the sequential version this is the case! However, when compiling with -tmt_pth, only the elements computed by the first thread are 42, the others are arbitrary. This can be made visible when uncommenting the print. This error appears consistently on sac2c 2.1.0-PuurGeluk-279-ge586b2 even when using -noprelude.