  We identify the obstructions for T-dualizing the boundary WZW model and make
explicit how they depend on the geometry of branes. In particular, the
obstructions disappear for certain brane configurations associated to
non-regular elements of the Cartan torus. It is shown in this case that the
boundary WZW model is "nested" in the twisted boundary WZW model as the
dynamical subsystem of the latter.
