One possibility is that the coatings of the camera reflects undesirable light into the front optical elements of the filter. On the off chance if there is no other optical surface that will reflect-back the light to the filter again, which is great. There are no halos other except the residual one, which are unavoidable depending on the filter design and quality. That is Baader the manufacturer means by their motto of "no radiances, no ghosting, no reflections".
Features: Baader ACF 2 DSLR Astro Conversion Filter for Canon EOS 350D/20D/10D
Specifications: Baader ACF 2 DSLR Astro Conversion Filter for Canon EOS 350D/20D/10D
Kit Contents:
Baader ACF 2 DSLR Astro Conversion Filter
User Guide
Manufacturer Warranty