diff --git a/core/include/traccc/fitting/kalman_filter/gain_matrix_updater.hpp b/core/include/traccc/fitting/kalman_filter/gain_matrix_updater.hpp
index 34ee9b3bb..e54b048ad 100644
--- a/core/include/traccc/fitting/kalman_filter/gain_matrix_updater.hpp
+++ b/core/include/traccc/fitting/kalman_filter/gain_matrix_updater.hpp
@@ -40,7 +40,7 @@ struct gain_matrix_updater {
     TRACCC_HOST_DEVICE inline bool operator()(
         const mask_group_t& /*mask_group*/, const index_t& /*index*/,
         track_state<algebra_t>& trk_state,
-        bound_track_parameters& bound_params) const {
+        const bound_track_parameters& bound_params) const {
 
         using shape_type = typename mask_group_t::value_type::shape;
 
@@ -63,7 +63,7 @@ struct gain_matrix_updater {
     template <size_type D, typename shape_t>
     TRACCC_HOST_DEVICE inline bool update(
         track_state<algebra_t>& trk_state,
-        bound_track_parameters& bound_params) const {
+        const bound_track_parameters& bound_params) const {
 
         static_assert(((D == 1u) || (D == 2u)),
                       "The measurement dimension should be 1 or 2");
@@ -138,9 +138,6 @@ struct gain_matrix_updater {
         // Wrap the phi in the range of [-pi, pi]
         wrap_phi(trk_state.filtered());
 
-        // Update the propagation flow
-        bound_params = trk_state.filtered();
-
         return true;
     }
 };
diff --git a/core/include/traccc/fitting/kalman_filter/kalman_actor.hpp b/core/include/traccc/fitting/kalman_filter/kalman_actor.hpp
index 4384c49de..7427b9244 100644
--- a/core/include/traccc/fitting/kalman_filter/kalman_actor.hpp
+++ b/core/include/traccc/fitting/kalman_filter/kalman_actor.hpp
@@ -75,13 +75,11 @@ struct kalman_actor : detray::actor {
         /// @return true if the iterator reaches the end of vector
         TRACCC_HOST_DEVICE
         bool is_complete() const {
-            /*
             if (!backward_mode && m_it == m_track_states.end()) {
                 return true;
             } else if (backward_mode && m_it_rev == m_track_states.rend()) {
                 return true;
             }
-            */
             return false;
         }
 
@@ -144,6 +142,9 @@ struct kalman_actor : detray::actor {
                 res = sf.template visit_mask<gain_matrix_updater<algebra_t>>(
                     trk_state, propagation._stepping.bound_params());
 
+                // Update the propagation flow
+                stepping.bound_params() = trk_state.filtered();
+
                 // Set full jacobian
                 trk_state.jacobian() = stepping.full_jacobian();
             }
diff --git a/core/include/traccc/fitting/kalman_filter/two_filters_smoother.hpp b/core/include/traccc/fitting/kalman_filter/two_filters_smoother.hpp
index 72f375b0f..a5aa2996f 100644
--- a/core/include/traccc/fitting/kalman_filter/two_filters_smoother.hpp
+++ b/core/include/traccc/fitting/kalman_filter/two_filters_smoother.hpp
@@ -154,7 +154,7 @@ struct two_filters_smoother {
             return false;
         }
 
-        // Update the propagation flow
+        // Update the bound track parameters
         bound_params.set_vector(filtered_vec);
         bound_params.set_covariance(filtered_cov);