... By means of deep optical images obtained at the Special Astrophysical Observatory 6-m telescope it was discovered that some Seyfert galaxies that were earlier considered to be non-interacting objects displayed signatures of elongated tidal envelopes belonging to satellite debris. ... Our results suggest that statistic studies based on popular imaging surveys (for example SDSS) can lead to an underestimation of the fraction of minor mergers among galaxies with active nuclei (AGN). ...