  We discuss the role of some nonpartonic effects which lead to $N_p^{\pi^+}
\ne N_n^{\pi^+}$ and $N_p^{\pi^-} \ne N_n^{\pi^-}$ and may therefore modify the
conclusionon the $\bar d - \bar u$ asymmetry extracted from semi-inclusive
production of pions in DIS. Quantitative estimations for resolved photon and
exclusive $\rho^0$ are given as examples. The results are discussed in the
context of recent HERMES data.
