I hope I can explain this, but in the future time frame, the Pasteur scans where the anomaly would be, thus triggering it. They get attacked and rescued by the Enterprise, which later goes back to where the anomaly is to stop it, but since it only moves backward through time, any moment further from when the Pasteur first initiated it, it wouldn't exist; and it certainly wouldn't be giving off any energy or whatever it was that the future Enterprise could stop. How do you explain that?