  A sublimating vicinal crystal surface can undergo a step bunching instability
when the attachment-detachment kinetics is asymmetric, in the sense of a normal
Ehrlich-Schwoebel effect. Here we investigate this instability in a model that
takes into account the subtle interplay between sublimation and step-step
interactions, which breaks the volume-conserving character of the dynamics
assumed in previous work. On the basis of a systematically derived continuum
equation for the surface profile, we argue that the non-conservative terms pose
a limitation on the size of emerging step bunches. This conclusion is supported
by extensive simulations of the discrete step dynamics, which show breakup of
large bunches into smaller ones as well as arrested coarsening and periodic
oscillations between states with different numbers of bunches.
