The results of computing a shock reflection are found to strongly depend on
the chosen coordinate system, Lagrangian or Eulerian. This is seen by comp
aring the amount of "wall heating" associated with the solutions to Noh's s
hock reflection problem computed in each reference frame. Here, an explanat
ion is offered that places a greater burden on the role of phase error or e
ffective wave speed in producing this effect. The reason for the greater di
fficulties in the Lagrangian frame are the non-uniformity of the mass coord
inates in a converging geometry. This produces a non-steady-state discrete
shock profile.