diff --git a/lib/Slic3r/Layer/Region.pm b/lib/Slic3r/Layer/Region.pm
index 6cbb58d20..8710bd880 100644
--- a/lib/Slic3r/Layer/Region.pm
+++ b/lib/Slic3r/Layer/Region.pm
@@ -447,6 +447,10 @@ sub _fill_gaps {
 sub prepare_fill_surfaces {
     my $self = shift;
     
+    # Note: in order to make the psPrepareInfill step idempotent, we should never
+    # alter fill_surfaces boundaries on which our idempotency relies since that's
+    # the only meaningful information returned by psPerimeters.
+    
     # if no solid layers are requested, turn top/bottom surfaces to internal
     if ($self->config->top_solid_layers == 0) {
         $_->surface_type(S_TYPE_INTERNAL) for @{$self->fill_surfaces->filter_by_type(S_TYPE_TOP)};
diff --git a/lib/Slic3r/Print.pm b/lib/Slic3r/Print.pm
index 51b31a675..fab5d818a 100644
--- a/lib/Slic3r/Print.pm
+++ b/lib/Slic3r/Print.pm
@@ -80,7 +80,10 @@ sub apply_config {
     # All regions now have distinct settings.
     # Check whether applying the new region config defaults we'd get different regions.
     my $rearrange_regions = 0;
+    my @other_region_configs = ();
     REGION: foreach my $region_id (0..($self->region_count - 1)) {
+        my $region = $self->regions->[$region_id];
+        my @this_region_configs = ();
         foreach my $object (@{$self->objects}) {
             foreach my $volume_id (@{ $object->get_region_volumes($region_id) }) {
                 my $volume = $object->model_object->volumes->[$volume_id];
@@ -96,17 +99,40 @@ sub apply_config {
                     $material_config->normalize;
                     $new->apply_dynamic($material_config);
                 }
-                if (!$new->equals($self->regions->[$region_id]->config)) {
+                if (defined first { !$_->equals($new) } @this_region_configs) {
+                    # if the new config for this volume differs from the other
+                    # volume configs currently associated to this region, it means
+                    # the region subdivision does not make sense anymore
                     $rearrange_regions = 1;
                     last REGION;
                 }
+                push @this_region_configs, $new;
+                
+                if (defined first { $_->equals($new) } @other_region_configs) {
+                    # if the new config for this volume equals any of the other
+                    # volume configs that are not currently associated to this
+                    # region, it means the region subdivision does not make
+                    # sense anymore
+                    $rearrange_regions = 1;
+                    last REGION;
+                }
+                
+                # if we're here and the new region config is different from the old
+                # one, we need to apply the new config and invalidate all objects
+                # (possible optimization: only invalidate objects using this region)
+                my $region_config_diff = $region->config->diff($new);
+                if (@$region_config_diff) {
+                    $region->config->apply($new);
+                    foreach my $o (@{$self->objects}) {
+                        $o->invalidate_all_steps
+                            if !$o->invalidate_state_by_config_options($region_config_diff);
+                    }
+                }
             }
         }
+        push @other_region_configs, @this_region_configs;
     }
     
-    # Some optimization is possible: if the volumes-regions mappings don't change
-    # but still region configs are changed somehow, we could just apply the diff
-    # and invalidate the affected steps.
     if ($rearrange_regions) {
         # the current subdivision of regions does not make sense anymore.
         # we need to remove all objects and re-add them
@@ -442,12 +468,14 @@ sub process {
                 while (defined (my $obj_layer = $q->dequeue)) {
                     my ($i, $region_id) = @$obj_layer;
                     my $layerm = $object->layers->[$i]->regions->[$region_id];
+                    $layerm->fills->clear;
                     $layerm->fills->append( $object->fill_maker->make_fill($layerm) );
                 }
             },
             collect_cb => sub {},
             no_threads_cb => sub {
                 foreach my $layerm (map @{$_->regions}, @{$object->layers}) {
+                    $layerm->fills->clear;
                     $layerm->fills->append($object->fill_maker->make_fill($layerm));
                 }
             },
diff --git a/lib/Slic3r/Print/Object.pm b/lib/Slic3r/Print/Object.pm
index 65456594f..1e0217c74 100644
--- a/lib/Slic3r/Print/Object.pm
+++ b/lib/Slic3r/Print/Object.pm
@@ -580,6 +580,10 @@ sub detect_surfaces_type {
         # clip surfaces to the fill boundaries
         foreach my $layer (@{$self->layers}) {
             my $layerm = $layer->regions->[$region_id];
+            
+            # Note: this method should be idempotent, but fill_surfaces gets modified 
+            # in place. However we're now only using its boundaries (which are invariant)
+            # so we're safe
             my $fill_boundaries = [ map $_->clone->p, @{$layerm->fill_surfaces} ];
             $layerm->fill_surfaces->clear;
             foreach my $surface (@{$layerm->slices}) {
diff --git a/xs/src/Print.cpp b/xs/src/Print.cpp
index bd957a41a..950377db1 100644
--- a/xs/src/Print.cpp
+++ b/xs/src/Print.cpp
@@ -198,9 +198,14 @@ PrintObject::invalidate_state_by_config_options(const std::vector<t_config_optio
 {
     std::set<PrintObjectStep> steps;
     
-    // this method only accepts PrintObjectConfig option keys
+    // this method only accepts PrintObjectConfig and PrintRegionConfig option keys
     for (std::vector<t_config_option_key>::const_iterator opt_key = opt_keys.begin(); opt_key != opt_keys.end(); ++opt_key) {
-        if (*opt_key == "perimeters") {
+        if (*opt_key == "perimeters"
+            || *opt_key == "extra_perimeters"
+            || *opt_key == "gap_fill_speed"
+            || *opt_key == "overhangs"
+            || *opt_key == "perimeter_extrusion_width"
+            || *opt_key == "thin_walls") {
             steps.insert(posPerimeters);
         } else if (*opt_key == "resolution"
             || *opt_key == "layer_height"
@@ -210,8 +215,10 @@ PrintObject::invalidate_state_by_config_options(const std::vector<t_config_optio
             steps.insert(posSlice);
         } else if (*opt_key == "support_material"
             || *opt_key == "support_material_angle"
+            || *opt_key == "support_material_extruder"
             || *opt_key == "support_material_extrusion_width"
             || *opt_key == "support_material_interface_layers"
+            || *opt_key == "support_material_interface_extruder"
             || *opt_key == "support_material_interface_spacing"
             || *opt_key == "support_material_interface_speed"
             || *opt_key == "support_material_pattern"
@@ -220,8 +227,28 @@ PrintObject::invalidate_state_by_config_options(const std::vector<t_config_optio
             || *opt_key == "dont_support_bridges") {
             steps.insert(posSupportMaterial);
         } else if (*opt_key == "interface_shells"
-            || *opt_key == "infill_only_where_needed") {
+            || *opt_key == "infill_only_where_needed"
+            || *opt_key == "bottom_solid_layers"
+            || *opt_key == "top_solid_layers"
+            || *opt_key == "infill_extruder"
+            || *opt_key == "infill_extrusion_width") {
             steps.insert(posPrepareInfill);
+        } else if (*opt_key == "fill_angle"
+            || *opt_key == "fill_pattern"
+            || *opt_key == "solid_fill_pattern"
+            || *opt_key == "infill_every_layers"
+            || *opt_key == "solid_infill_below_area"
+            || *opt_key == "solid_infill_every_layers"
+            || *opt_key == "top_infill_extrusion_width") {
+            steps.insert(posInfill);
+        } else if (*opt_key == "fill_density"
+            || *opt_key == "solid_infill_extrusion_width") {
+            steps.insert(posPerimeters);
+            steps.insert(posPrepareInfill);
+        } else if (*opt_key == "external_perimeter_extrusion_width"
+            || *opt_key == "perimeter_extruder") {
+            steps.insert(posPerimeters);
+            steps.insert(posSupportMaterial);
         } else {
             // for legacy, if we can't handle this option let's signal the caller to invalidate all steps
             return false;