Constitutive models for fiber-reinforced ceramic-matrix composites (CMCs) are needed to enable implementation of these materials in future engineering systems. One such constitutive model, developed by Genin and Hutchinson [1], is based on a phenomenological description of the inelastic response of CMC laminates. Although the model has found some utility in elucidating the role of inelasticity in stress re-distribution around strain concentrating features, we find that, in some instances, finite element analyses based on this model exhibit numerical convergence problems. In the present study, we demonstrate both analytically and by finite element analyses that, for certain anisotropic laminates, these numerical issues stem from the fact that the model formulation is unstable. Additionally, we propose and assess modifications to the formulation that mitigate these problems yet retain the positive features of the original model. The expectation is that the modifications will enable broader utilization of the model within the engineering design community.