  We develop the pQCD description of the diffraction dissociation (DD) of
longitudinal photons. We demonstrate that the longitudinal diffractive
structure function does not factor into the flux of pomerons and the partonic
structure function of the pomeron, thus defying the usually assumed Regge
factorization. In contrast to DD of the transverse photons, DD of the
longitudinal photons is strongly peaked at $\beta =1$. We comment on duality
properties of DD in deep inelastic scattering.
