The long-time relaxation of the dynamic surface tension (DST) in aqueous solutions of four structural isomers of butyl alcohol has been observed with the aid of the maximum bubble pressure technique. Diffusion-controlled kinetics was found to allow an apparently successful (in terms of the quality of fitting) description of the observed DST dynamics, but it leads to an unrealistically low value of the diffusion coefficient, 10-11-10-13 m2 s-1. Conversely, the activation-controlled kinetics fails to explain the slow damping of DST curves observed over long time periods. A comprehensive theoretical analysis supported by numerical simulations has conclusively shown that neither diffusion nor mixed diffusion-activation kinetics can adequately account for the observed slower DST relaxation. As an alternative explanation, the presence of packing defects in the adsorbed layer is proposed.