Why? Is it violating some principle of QM?
Ok what if we change the experiment a little. What if we made the thing symmetric across V1 and V2 so that we are generating one interference pattern with S1 and S2 and another interference pattern with I1 and I2. This should be possible as long as the path lengths are equal. Now if we block I1 it will stop interference at Di. But it should also stop interference at Ds. But I1 never goes through NL2 here.
I would really like to get an understanding of this experiment nailed. I have been trying since I first saw it in scientific american years ago.