diff --git a/xs/src/libslic3r/Model.cpp b/xs/src/libslic3r/Model.cpp
index 93f0152c8..19c474cad 100644
--- a/xs/src/libslic3r/Model.cpp
+++ b/xs/src/libslic3r/Model.cpp
@@ -1016,6 +1016,11 @@ BoundingBoxf3 ModelInstance::transform_bounding_box(const BoundingBoxf3 &bbox, b
     return bbox.transformed(world_matrix(dont_translate));
 }
 
+Vec3d ModelInstance::transform_vector(const Vec3d& v, bool dont_translate) const
+{
+    return world_matrix(dont_translate) * v;
+}
+
 void ModelInstance::transform_polygon(Polygon* polygon) const
 {
     polygon->rotate(this->rotation);                // rotate around polygon origin
diff --git a/xs/src/libslic3r/Model.hpp b/xs/src/libslic3r/Model.hpp
index bbfd2bde2..8a8af481c 100644
--- a/xs/src/libslic3r/Model.hpp
+++ b/xs/src/libslic3r/Model.hpp
@@ -239,6 +239,8 @@ public:
     BoundingBoxf3 transform_mesh_bounding_box(const TriangleMesh* mesh, bool dont_translate = false) const;
     // Transform an external bounding box.
     BoundingBoxf3 transform_bounding_box(const BoundingBoxf3 &bbox, bool dont_translate = false) const;
+    // Transform an external vector.
+    Vec3d transform_vector(const Vec3d& v, bool dont_translate = false) const;
     // To be called on an external polygon. It does not translate the polygon, only rotates and scales.
     void transform_polygon(Polygon* polygon) const;
 
diff --git a/xs/src/slic3r/GUI/GLCanvas3D.cpp b/xs/src/slic3r/GUI/GLCanvas3D.cpp
index 063b96cbe..2bec6b66b 100644
--- a/xs/src/slic3r/GUI/GLCanvas3D.cpp
+++ b/xs/src/slic3r/GUI/GLCanvas3D.cpp
@@ -5241,11 +5241,14 @@ void GLCanvas3D::_on_move(const std::vector<int>& volume_idxs)
         {
             // Move a regular object.
             ModelObject* model_object = m_model->objects[obj_idx];
-            const Vec3d& offset = volume->get_offset();
-            model_object->instances[instance_idx]->offset = Vec2d(offset(0), offset(1));
-            model_object->invalidate_bounding_box();
-            update_position_values();
-            object_moved = true;
+            if (model_object != nullptr)
+            {
+                const Vec3d& offset = volume->get_offset();
+                model_object->instances[instance_idx]->offset = Vec2d(offset(0), offset(1));
+                model_object->invalidate_bounding_box();
+                update_position_values();
+                object_moved = true;
+            }
         }
         else if (obj_idx == 1000)
             // Move a wipe tower proxy.
diff --git a/xs/src/slic3r/GUI/GLGizmo.cpp b/xs/src/slic3r/GUI/GLGizmo.cpp
index e46cfa925..1c0456fa8 100644
--- a/xs/src/slic3r/GUI/GLGizmo.cpp
+++ b/xs/src/slic3r/GUI/GLGizmo.cpp
@@ -1061,8 +1061,6 @@ void GLGizmoFlatten::on_render_for_picking(const BoundingBoxf3& box) const
 
     for (unsigned int i = 0; i < m_planes.size(); ++i)
     {
-        // FIXME: the color assignement will fail if the planes count is greater than 254
-        //        use the other color components in that case !!
         ::glColor3f(1.0f, 1.0f, picking_color_component(i));
         for (const Vec2d& offset : m_instances_positions) {
             ::glPushMatrix();
@@ -1240,9 +1238,9 @@ void GLGizmoFlatten::update_planes()
         polygon = transform(polygon, m);
     }
 
-    // We'll sort the planes by area and only keep the 255 largest ones (because of the picking pass limitations):
+    // We'll sort the planes by area and only keep the 254 largest ones (because of the picking pass limitations):
     std::sort(m_planes.rbegin(), m_planes.rend(), [](const PlaneData& a, const PlaneData& b) { return a.area < b.area; });
-    m_planes.resize(std::min((int)m_planes.size(), 255));
+    m_planes.resize(std::min((int)m_planes.size(), 254));
 
     // Planes are finished - let's save what we calculated it from:
     m_source_data.bounding_boxes.clear();