Streaky dark scan areas

The Scan Guide says it all: Do not use dark originals or images with black. I now know why. The dark areas are mud. With bright images of this mud is not as apparent, but in dark areas, it just looks awful. In 2013 unacceptable quality. From the idea practical, but unusable because of the quality. Even after calibration, and sensor cleaning Walzen.- no change (even though I had only 5 images scanned). I have much experience .. scan from flatbed scanner up to the slides. But I never had a bad quality.