diff --git a/lib/Slic3r/GUI/SkeinPanel.pm b/lib/Slic3r/GUI/SkeinPanel.pm
index b2d92bdfa..6189b8c55 100644
--- a/lib/Slic3r/GUI/SkeinPanel.pm
+++ b/lib/Slic3r/GUI/SkeinPanel.pm
@@ -158,7 +158,7 @@ sub do_slice {
         {
             local $SIG{__WARN__} = sub {
                 my $message = shift;
-                Wx::MessageDialog->new($self, $message, 'Non-manifold object', 
+                Wx::MessageDialog->new($self, $message, 'Warning', 
                     wxOK | wxICON_WARNING)->ShowModal;
             };
             $skein->go;
diff --git a/lib/Slic3r/Layer.pm b/lib/Slic3r/Layer.pm
index 10e0a2ce4..04baf705c 100644
--- a/lib/Slic3r/Layer.pm
+++ b/lib/Slic3r/Layer.pm
@@ -266,14 +266,14 @@ sub process_bridges {
             my $bridge_over_hole = 0;
             my @edges = ();  # edges are POLYLINES
             foreach my $supporting_surface (@supporting_surfaces) {
-                my @surface_edges = $supporting_surface->contour->clip_with_polygon($contour_offset);
+                my @surface_edges = map $_->clip_with_polygon($contour_offset),
+                    ($supporting_surface->contour, @{$supporting_surface->holes});
+                
                 if (@supporting_surfaces == 1 && @surface_edges == 1
                     && @{$supporting_surface->contour->p} == @{$surface_edges[0]->p}) {
                     $bridge_over_hole = 1;
-                } else {
-                    @surface_edges = grep { @{$_->points} } @surface_edges;
                 }
-                push @edges, @surface_edges;
+                push @edges, grep { @{$_->points} } @surface_edges;
             }
             Slic3r::debugf "  Bridge is supported on %d edge(s)\n", scalar(@edges);
             Slic3r::debugf "  and covers a hole\n" if $bridge_over_hole;
diff --git a/lib/Slic3r/Perimeter.pm b/lib/Slic3r/Perimeter.pm
index 99feac927..40402b070 100644
--- a/lib/Slic3r/Perimeter.pm
+++ b/lib/Slic3r/Perimeter.pm
@@ -34,15 +34,14 @@ sub make_perimeter {
     ])};
     
     foreach my $surface (@surfaces) {
-        # the outer loop must be offsetted by half extrusion width inwards
         my @last_offsets = ($surface->expolygon);
-        my $distance = scale $Slic3r::flow_width / 2;
+        my $distance = 0;
         
         # create other offsets
         push @perimeters, [];
         for (my $loop = 0; $loop < $Slic3r::perimeters; $loop++) {
             # offsetting a polygon can result in one or many offset polygons
-            @last_offsets = map $_->offset_ex(-$distance), @last_offsets;
+            @last_offsets = map $_->offset_ex(-$distance), @last_offsets if $distance;
             push @{ $perimeters[-1] }, [@last_offsets];
             
             # offset distance for inner loops
diff --git a/lib/Slic3r/Print.pm b/lib/Slic3r/Print.pm
index 0c9bc4fc9..1b72b6302 100644
--- a/lib/Slic3r/Print.pm
+++ b/lib/Slic3r/Print.pm
@@ -181,6 +181,20 @@ sub detect_surfaces_type {
             @$expolygons;
     };
     
+    # the contours must be offsetted by half extrusion width inwards
+    {
+        my $distance = scale $Slic3r::flow_width / 2;
+        foreach my $layer (@{$self->layers}) {
+            my @surfaces = @{$layer->slices};
+            @{$layer->slices} = ();
+            foreach my $surface (@surfaces) {
+                push @{$layer->slices}, map Slic3r::Surface->cast_from_expolygon
+                    ($_, surface_type => 'internal'),
+                    $surface->expolygon->offset_ex(-$distance);
+            }
+        }
+    }
+    
     for (my $i = 0; $i < $self->layer_count; $i++) {
         my $layer = $self->layers->[$i];
         Slic3r::debugf "Detecting solid surfaces for layer %d\n", $layer->id;