  There is strong observational evidence of shocks and clumping in
radiation-driven stellar winds from hot, luminous stars. The resulting non
monotonic velocity law allows for radiative coupling between distant locations,
which is so far not accounted for in hydrodynamic wind simulations. In the
present paper, we determine the Sobolev source function and radiative line
force in the presence of radiative coupling in spherically symmetric flows,
extending the geometry-free formalism of Rybicki and Hummer (1978) to the case
of three-point coupling, which can result from, e.g., corotating interaction
regions, wind shocks, or mass overloading. For a simple model of an overloaded
wind, we find that, surprisingly, the flow decelerates at all radii above a
certain height when nonlocal radiative coupling is accounted for. We discuss
whether radiation-driven winds might in general not be able to re-accelerate
after a non monotonicity has occurred in the velocity law.
