  We study Pomeron-Odderon interference effects giving rise to charge and
single-spin asymmetries in diffractive electroproduction of a $\pi^+ \pi^-$
pair. The final state interactions and the role of $f_0$ meson are discussed.
The absence of $f_0$ signal in the charge asymmetry observed by HERMES may be
due to the smalness of its quark component.
