For every parameter vector the BK conditions are satisfied in estimation. But the estimation result is none of these parameters. It is not the median, but the mean. The mean is a convex combination of the estimated parameters. If the stability region is a convex set of the parameters, this particular convex-combination called mean will be inside the stability region. However, in some cases the stability region is not a convex set and the mean parameter vector is outside of it. In these cases, stoch_simul after estimation will crash because the BK-conditions are violated.