Reply To: Overprint will solve?

There may have been other issues with your file that required the printer to globally knock out black at the RIP, or perhaps that is their default protocol (there are occasions where overprinting black produces undesirable results, such as a large black box sitting overtop a portion of an image and if the black overprints, you’ll see a density difference where the image is).

Still, even if they knocked it out on purpose, there should be trapping applied to minimize misregistration.