  We review in generality why time-independent endstates can be reached in
black hole and collapse simulations, with and without excision. We characterise
the Killing states of the Bona-Masso slicing condition with time derivative
along the normals to the slice ("BMn") as solutions of a mixed
elliptic/hyperbolic differential equation on the slice. We show numerically
that these steady states can be reached as end states from typical initial data
with excision but can be reached with the puncture method only if the puncture
is not numerically well resolved. During the evolution, BMn slicings often form
gauge shocks. It may be that these are not seen in current 3D simulations only
through lack of resolution, although we expect that they can be avoided with
some care. Finally we point out that excision with BMn as currently implemented
is ill-posed and therefore not expected to converge; this can be cured. In
technical appendixes, we derive the equations of pure gauge systems on a fixed
spacetime, and bring the BSSN/NOR equations into 3-dimensional tensor form
suitable for multiple coordinate patches or spherical polar coordinates.
