  The presentation is concerned with higher twist corrections of nonpartonic
origin to semi-inclusive observables in the kinematical region relevant for the
HERMES experiment. We demonstrate a strong impact of the VDM-like interaction
and the exclusive production of $\rho^0$ meson on the extraction of the $\bar d
- \bar u$ asymmetry from charged pion DIS multiplicities. We also show that it
is the exclusive-$\rho^0$ channel which accounts for the experimentally
observed effect of the excess of charged over neutral pions produced at large
$z$.
