The active model has been proven to be unbounded. The notion of unboundedness adopted by IloCplex
is technically that of dual infeasibility; this does not include the notion that the model has been proven to be feasible. Instead, what has been proven is that if there is a feasible solution with objective value z*, there exists a feasible solution with objective value z*-1 for a minimization problem, or z*+1 for a maximization problem.