  We report the computation of the matrix element of the chromomagnetic
operator of the flavour changing neutral current (FCNC)-type between a $B$- or
$D$-meson state and a light hadron and off-shell photon. The computation is
carried out by using the method of light-cone sum rules (LCSR). It is found
that the matrix element exhibits a large strong phase for which we give a long
distance interpretation. The analytic structure of the correlation function in
use admits a complex anomalous threshold on the physical sheet, the meaning and
handling of which within the sum rule approach is discussed. We compare our
results to QCD factorisation for which spectator photon emission is end-point
divergent.
