diff --git a/lib/Slic3r/GUI/Plater.pm b/lib/Slic3r/GUI/Plater.pm
index 08dbaddef..1a2d324ba 100644
--- a/lib/Slic3r/GUI/Plater.pm
+++ b/lib/Slic3r/GUI/Plater.pm
@@ -223,7 +223,7 @@ sub new {
     });
     
     $self->_update_bed_size;
-    $self->recenter;
+    $self->update;
     
     {
         my $presets;
@@ -432,7 +432,7 @@ sub object_loaded {
     
     $self->make_thumbnail($obj_idx);
     $self->arrange unless $params{no_arrange};
-    $self->recenter;
+    $self->update;
     $self->{list}->Update;
     $self->{list}->Select($obj_idx, 1);
     $self->object_list_changed;
@@ -454,7 +454,7 @@ sub remove {
     $self->object_list_changed;
     
     $self->select_object(undef);
-    $self->recenter;
+    $self->update;
     $self->{canvas}->Refresh;
 }
 
@@ -504,7 +504,7 @@ sub decrease {
         $self->{list}->Select($obj_idx, 0);
         $self->{list}->Select($obj_idx, 1);
     }
-    $self->recenter;
+    $self->update;
     $self->{canvas}->Refresh;
 }
 
@@ -537,7 +537,7 @@ sub rotate {
         $object->transform_thumbnail($self->{model}, $obj_idx);
     }
     $self->selection_changed;  # refresh info (size etc.)
-    $self->recenter;
+    $self->update;
     $self->{canvas}->Refresh;
 }
 
@@ -584,7 +584,7 @@ sub arrange {
     };
     # ignore arrange warnings on purpose
     
-    $self->recenter;
+    $self->update;
     $self->{canvas}->Refresh;
 }
 
@@ -733,8 +733,8 @@ sub export_gcode2 {
     } if $Slic3r::have_threads;
     
     my $print = $self->{print};
-    $print->config->apply($config);
-    $print->extra_variables($extra_variables);
+    $print->apply_config($config);
+    $print->apply_extra_variables($extra_variables);
     
     eval {
         $print->config->validate;
@@ -746,10 +746,10 @@ sub export_gcode2 {
             
             $print->status_cb(sub { $params{progressbar}->(@_) });
             if ($params{export_svg}) {
-                $print->export_svg(%params);
+                $print->export_svg(output_file => $output_file);
             } else {
                 $print->process;
-                $print->export_gcode(%params);
+                $print->export_gcode(output_file => $output_file);
             }
             $print->status_cb(undef);
             Slic3r::GUI::warning_catcher($self, $Slic3r::have_threads ? sub {
@@ -849,7 +849,7 @@ sub on_thumbnail_made {
     my ($obj_idx) = @_;
     
     $self->{objects}[$obj_idx]->transform_thumbnail($self->{model}, $obj_idx);
-    $self->recenter;
+    $self->update;
     $self->{canvas}->Refresh;
 }
 
@@ -863,10 +863,19 @@ sub clean_instance_thumbnails {
 
 # this method gets called whenever print center is changed or the objects' bounding box changes
 # (i.e. when an object is added/removed/moved/rotated/scaled)
-sub recenter {
+sub update {
     my $self = shift;
     
     $self->{model}->center_instances_around_point($self->{config}->print_center);
+    
+    # sync model and print object instances
+    for my $obj_idx (0..$#{$self->{objects}}) {
+        my $model_object = $self->{model}->objects->[$obj_idx];
+        my $print_object = $self->{print}->objects->[$obj_idx];
+        
+        $print_object->delete_all_copies;
+        $print_object->add_copy(@{$_->offset}) for @{$model_object->instances};
+    }
 }
 
 sub on_config_change {
@@ -892,7 +901,7 @@ sub on_config_change {
     } elsif ($self->{config}->has($opt_key)) {
         $self->{config}->set($opt_key, $value);
         $self->_update_bed_size if $opt_key eq 'bed_size';
-        $self->recenter if $opt_key eq 'print_center';
+        $self->update if $opt_key eq 'print_center';
     }
 }
 
@@ -904,7 +913,7 @@ sub _update_bed_size {
     # when the canvas is not rendered yet, its GetSize() method returns 0,0
     # scaling_factor is expressed in pixel / mm
     $self->{scaling_factor} = CANVAS_SIZE->[X] / max(@{ $self->{config}->bed_size });
-    $self->recenter;
+    $self->update;
 }
 
 # this is called on the canvas
@@ -992,7 +1001,7 @@ sub repaint {
             
             # if sequential printing is enabled and we have more than one object, draw clearance area
             if ($parent->{config}->complete_objects && (map @{$_->instances}, @{$parent->{model}->objects}) > 1) {
-                my ($clearance) = @{offset([$thumbnail->convex_hull], (scale($parent->{config}->extruder_clearance_radius) / 2), 0.0001, JT_ROUND)};
+                my ($clearance) = @{offset([$thumbnail->convex_hull], (scale($parent->{config}->extruder_clearance_radius) / 2), 1, JT_ROUND, scale(0.1))};
                 $dc->SetPen($parent->{clearance_pen});
                 $dc->SetBrush($parent->{transparent_brush});
                 $dc->DrawPolygon($parent->points_to_pixel($clearance, 1), 0, 0);
@@ -1004,7 +1013,8 @@ sub repaint {
     if (@{$parent->{objects}} && $parent->{config}->skirts) {
         my @points = map @{$_->contour}, map @$_, map @{$_->instance_thumbnails}, @{$parent->{objects}};
         if (@points >= 3) {
-            my ($convex_hull) = @{offset([convex_hull(\@points)], scale($parent->{config}->skirt_distance), 0.0001, JT_ROUND)};
+            my @o = @{Slic3r::Geometry::Clipper::simplify_polygons([convex_hull(\@points)])};
+            my ($convex_hull) = @{offset([convex_hull(\@points)], scale($parent->{config}->skirt_distance), 1, JT_ROUND, scale(0.1))};
             $dc->SetPen($parent->{skirt_pen});
             $dc->SetBrush($parent->{transparent_brush});
             $dc->DrawPolygon($parent->points_to_pixel($convex_hull, 1), 0, 0);
@@ -1041,7 +1051,7 @@ sub mouse_event {
         }
         $parent->Refresh;
     } elsif ($event->ButtonUp(&Wx::wxMOUSE_BTN_LEFT)) {
-        $parent->recenter;
+        $parent->update;
         $parent->Refresh;
         $self->{drag_start_pos} = undef;
         $self->{drag_object} = undef;
diff --git a/lib/Slic3r/Print.pm b/lib/Slic3r/Print.pm
index eff01d8e7..b68758587 100644
--- a/lib/Slic3r/Print.pm
+++ b/lib/Slic3r/Print.pm
@@ -10,7 +10,7 @@ use Slic3r::Geometry qw(X Y Z X1 Y1 X2 Y2 MIN MAX PI scale unscale move_points c
 use Slic3r::Geometry::Clipper qw(diff_ex union_ex union_pt intersection_ex intersection offset
     offset2 union union_pt_chained JT_ROUND JT_SQUARE);
 
-has 'config'                 => (is => 'rw', default => sub { Slic3r::Config->new_from_defaults }, trigger => 1);
+has 'config'                 => (is => 'rw', default => sub { Slic3r::Config->new_from_defaults }, trigger => \&init_config);
 has 'extra_variables'        => (is => 'rw', default => sub {{}});
 has 'objects'                => (is => 'rw', default => sub {[]});
 has 'status_cb'              => (is => 'rw');
@@ -30,10 +30,11 @@ sub BUILD {
     my $self = shift;
     
     # call this manually because the 'default' coderef doesn't trigger the trigger
-    $self->_trigger_config;
+    $self->init_config;
 }
 
-sub _trigger_config {
+# this method needs to be idempotent
+sub init_config {
     my $self = shift;
     
     # store config in a handy place
@@ -67,6 +68,14 @@ sub _trigger_config {
     $self->config->set('retract_lift', [ map $self->config->retract_lift->[0], @{$self->config->retract_lift} ]);
 }
 
+sub apply_config {
+    my ($self, $config) = @_;
+    
+    $self->config->apply($config);
+    $self->init_config;
+    $_->init_config for @{$self->objects};
+}
+
 sub _build_has_support_material {
     my $self = shift;
     return (first { $_->config->support_material } @{$self->objects})
@@ -165,7 +174,7 @@ sub validate {
                 $convex_hull->translate(@{$object->_copies_shift});
                 
                 # grow convex hull with the clearance margin
-                ($convex_hull) = @{offset([$convex_hull], scale $self->config->extruder_clearance_radius / 2, 1, JT_ROUND)};
+                ($convex_hull) = @{offset([$convex_hull], scale $self->config->extruder_clearance_radius / 2, 1, JT_ROUND, scale(0.1))};
                 
                 # now we need that no instance of $convex_hull does not intersect any of the previously checked object instances
                 for my $copy (@{$object->_shifted_copies}) {
@@ -552,6 +561,8 @@ sub make_skirt {
     return unless $Slic3r::Config->skirts > 0
         || ($Slic3r::Config->ooze_prevention && @{$self->extruders} > 1);
     
+    $self->skirt->clear;  # method must be idempotent
+    
     # collect points from all layers contained in skirt height
     my @points = ();
     foreach my $obj_idx (0 .. $#{$self->objects}) {
@@ -587,7 +598,7 @@ sub make_skirt {
     my $distance = scale $Slic3r::Config->skirt_distance;
     for (my $i = $Slic3r::Config->skirts; $i > 0; $i--) {
         $distance += scale $spacing;
-        my $loop = offset([$convex_hull], $distance, 0.0001, JT_ROUND)->[0];
+        my $loop = offset([$convex_hull], $distance, 1, JT_ROUND, scale(0.1))->[0];
         $self->skirt->append(Slic3r::ExtrusionLoop->new(
             polygon         => Slic3r::Polygon->new(@$loop),
             role            => EXTR_ROLE_SKIRT,
@@ -615,6 +626,8 @@ sub make_brim {
     my $self = shift;
     return unless $Slic3r::Config->brim_width > 0;
     
+    $self->brim->clear;  # method must be idempotent
+    
     my $flow = $self->objects->[0]->layers->[0]->regions->[0]->perimeter_flow;
     
     my $grow_distance = $flow->scaled_width / 2;
@@ -915,7 +928,6 @@ sub expanded_output_filepath {
     } else {
         # path is a full path to a file so we use it as it is
     }
-    
     return $self->config->replace_options($path, { %{$self->extra_variables}, %$extra_variables });
 }
 
@@ -928,4 +940,9 @@ sub parse_filename {
     return ($filename, $filename_base);
 }
 
+sub apply_extra_variables {
+    my ($self, $extra) = @_;
+    $self->extra_variables->{$_} = $extra->{$_} for keys %$extra;
+}
+
 1;
diff --git a/lib/Slic3r/Print/Object.pm b/lib/Slic3r/Print/Object.pm
index 9936a3036..44b74c6be 100644
--- a/lib/Slic3r/Print/Object.pm
+++ b/lib/Slic3r/Print/Object.pm
@@ -85,6 +85,12 @@ sub delete_last_copy {
     $self->_trigger_copies;
 }
 
+sub delete_all_copies {
+    my ($self) = @_;
+    @{$self->copies} = ();
+    $self->_trigger_copies;
+}
+
 sub init_config {
     my $self = shift;
     $self->config(Slic3r::Config->merge($self->print->config, $self->config_overrides));