diff --git a/lib/Slic3r/Print/Object.pm b/lib/Slic3r/Print/Object.pm
index 5fb759b3b..da51615b5 100644
--- a/lib/Slic3r/Print/Object.pm
+++ b/lib/Slic3r/Print/Object.pm
@@ -606,7 +606,8 @@ sub discover_horizontal_shells {
                     next if $n < 0 || $n >= $self->layer_count;
                     Slic3r::debugf "  looking for neighbors on layer %d...\n", $n;
                     
-                    my @neighbor_fill_surfaces = @{$self->layers->[$n]->regions->[$region_id]->fill_surfaces};
+                    my $neighbor_fill_surfaces = $self->layers->[$n]->regions->[$region_id]->fill_surfaces;
+                    my @neighbor_fill_surfaces = map $_->clone, @$neighbor_fill_surfaces;  # clone because we will use these surfaces even after clearing the collection
                     
                     # find intersection between neighbor and current layer's surfaces
                     # intersections have contours and holes
@@ -679,7 +680,6 @@ sub discover_horizontal_shells {
                         scalar(@$internal_solid), scalar(@$internal);
                     
                     # assign resulting internal surfaces to layer
-                    my $neighbor_fill_surfaces = $self->layers->[$n]->regions->[$region_id]->fill_surfaces;
                     $neighbor_fill_surfaces->clear;
                     $neighbor_fill_surfaces->append(map Slic3r::Surface->new
                         (expolygon => $_, surface_type => S_TYPE_INTERNAL), @$internal);
diff --git a/xs/src/myinit.h b/xs/src/myinit.h
index e3e143ee8..5d1c17a17 100644
--- a/xs/src/myinit.h
+++ b/xs/src/myinit.h
@@ -3,6 +3,7 @@
 
 // this needs to be included early for MSVC (listing it in Build.PL is not enough)
 #include <ostream>
+#include <iostream>
 
 extern "C" {
 #include "EXTERN.h"
@@ -18,4 +19,40 @@ extern "C" {
 namespace Slic3r {}
 using namespace Slic3r;
 
+/* Implementation of CONFESS("foo"): */
+#define CONFESS(...) \
+     confess_at(__FILE__, __LINE__, __func__, __VA_ARGS__)
+
+void
+do_confess(SV *error_sv)
+{
+     dSP;
+     ENTER;
+     SAVETMPS;
+     PUSHMARK(SP);
+     XPUSHs( sv_2mortal(error_sv) );
+     PUTBACK;
+     call_pv("Carp::confess", G_DISCARD);
+     FREETMPS;
+     LEAVE;
+}
+
+void
+confess_at(const char *file, int line, const char *func,
+            const char *pat, ...)
+{
+     va_list args;
+     SV *error_sv = newSVpvf("Error in function %s at %s:%d: ", func,
+         file, line);
+
+     va_start(args, pat);
+     sv_vcatpvf(error_sv, pat, &args);
+     va_end(args);
+
+     sv_catpvn(error_sv, "\n\t", 2);
+
+     do_confess(error_sv);
+}
+/* End implementation of CONFESS("foo") */
+
 #endif