Fixed cutting of objects in left oriented coordinate space.

Removed some spurious debugging printf.

src/libslic3r/Model.cpp

@@ -1187,8 +1187,9 @@ ModelObjectPtrs ModelObject::cut(size_t instance, coordf_t z, bool keep_upper, b
         else {
             TriangleMesh upper_mesh, lower_mesh;
 
-            // Transform the mesh by the combined transformation matrix
-            volume->mesh.transform(instance_matrix * volume_matrix);
+            // Transform the mesh by the combined transformation matrix.
+            // Flip the triangles in case the composite transformation is left handed.
+            volume->mesh.transform(instance_matrix * volume_matrix, true);
 
             // Perform cut
             TriangleMeshSlicer tms(&volume->mesh);

src/slic3r/GUI/GUI_ObjectList.cpp

@@ -507,7 +507,6 @@ void ObjectList::key_event(wxKeyEvent& event)
         || event.GetKeyCode() == WXK_BACK
 #endif //__WXOSX__
         ) {
-        printf("WXK_BACK\n");
         remove();
     }
     else if (wxGetKeyState(wxKeyCode('A')) && wxGetKeyState(WXK_SHIFT))