diff --git a/src/opt/opt_solver.cpp b/src/opt/opt_solver.cpp
index ee91b06a491..955025fd96c 100644
--- a/src/opt/opt_solver.cpp
+++ b/src/opt/opt_solver.cpp
@@ -52,7 +52,7 @@ namespace opt {
         if (m_params.m_case_split_strategy == CS_ACTIVITY_DELAY_NEW) {            
             m_params.m_relevancy_lvl = 0;
         }
-        m_params.m_arith_auto_config_simplex = false;
+        m_params.m_arith_auto_config_simplex = true;
         m_params.m_threads = 1; // need to interact with the solver that created model so can't have threads
         // m_params.m_auto_config = false;
     }
@@ -67,7 +67,7 @@ namespace opt {
         m_dump_benchmarks = p.dump_benchmarks();
         m_params.updt_params(_p);
         m_context.updt_params(_p);
-        m_params.m_arith_auto_config_simplex = false;
+        m_params.m_arith_auto_config_simplex = true;
     }
 
     solver* opt_solver::translate(ast_manager& m, params_ref const& p) {
diff --git a/src/smt/theory_arith_pp.h b/src/smt/theory_arith_pp.h
index b0d43bc00ac..edc640d86aa 100644
--- a/src/smt/theory_arith_pp.h
+++ b/src/smt/theory_arith_pp.h
@@ -83,9 +83,11 @@ namespace smt {
 
     template<typename Ext>
     void theory_arith<Ext>::display_row(std::ostream & out, row const & r, bool compact) const {
-
+        if (static_cast<unsigned>(r.get_base_var()) >= m_columns.size())
+            return;
         column const & c   = m_columns[r.get_base_var()];
-        out << "(v" << r.get_base_var() << " r" << c[0].m_row_id << ") : ";
+        if (c.size() > 0)
+            out << "(v" << r.get_base_var() << " r" << c[0].m_row_id << ") : ";
         bool first = true;
         for (auto const& e : r) {
             if (!e.is_dead()) {