diff --git a/src/libslic3r/GCode/GCodeProcessor.cpp b/src/libslic3r/GCode/GCodeProcessor.cpp
index e34e4e5dda..d0c9962900 100644
--- a/src/libslic3r/GCode/GCodeProcessor.cpp
+++ b/src/libslic3r/GCode/GCodeProcessor.cpp
@@ -3610,7 +3610,7 @@ void GCodeProcessor::post_process()
                     last_time_insertion = rev_it->time;
                     const std::string out_line = line_inserter(i + 1, last_time_insertion, m_time - last_time_insertion);
                     rev_it_dist = std::distance(m_lines.rbegin(), rev_it) + 1;
-                    const auto new_it = m_lines.insert(rev_it.base(), { out_line, rev_it->time });
+                    m_lines.insert(rev_it.base(), { out_line, rev_it->time });
 #ifndef NDEBUG
                     m_statistics.add_line(out_line.length());
 #endif // NDEBUG
@@ -3984,7 +3984,7 @@ void GCodeProcessor::post_process()
 
 #if ENABLE_GCODE_POSTPROCESS_BACKTRACE
     // add lines XXX to exported gcode
-      auto process_line_T = [this, &export_lines](const std::string& gcode_line, const size_t g1_lines_counter, const ExportLines::Backtrace& backtrace) {
+    auto process_line_T = [this, &export_lines](const std::string& gcode_line, const size_t g1_lines_counter, const ExportLines::Backtrace& backtrace) {
         const std::string cmd = GCodeReader::GCodeLine::extract_cmd(gcode_line);
         if (cmd.size() >= 2) {
             std::stringstream ss(cmd.substr(1));
diff --git a/src/slic3r/GUI/3DScene.cpp b/src/slic3r/GUI/3DScene.cpp
index 97975404ff..b4e3936daf 100644
--- a/src/slic3r/GUI/3DScene.cpp
+++ b/src/slic3r/GUI/3DScene.cpp
@@ -593,7 +593,7 @@ void GLVolumeCollection::load_object_auxiliary(
         return;
     const Transform3d mesh_trafo_inv = print_object->trafo().inverse();
 
-    auto add_volume = [this, &instances, timestamp](int obj_idx, int inst_idx, const ModelInstance& model_instance, SLAPrintObjectStep step,
+    auto add_volume = [this, timestamp](int obj_idx, int inst_idx, const ModelInstance& model_instance, SLAPrintObjectStep step,
         const TriangleMesh& mesh, const ColorRGBA& color, std::optional<const TriangleMesh> convex_hull = std::nullopt) {
         if (mesh.empty())
             return;
diff --git a/src/slic3r/GUI/GLCanvas3D.cpp b/src/slic3r/GUI/GLCanvas3D.cpp
index d04fc7f985..72aaa59448 100644
--- a/src/slic3r/GUI/GLCanvas3D.cpp
+++ b/src/slic3r/GUI/GLCanvas3D.cpp
@@ -3189,6 +3189,10 @@ void GLCanvas3D::on_mouse(wxMouseEvent& evt)
         m_canvas->SetFocus();
 
     if (evt.Entering()) {
+        if (m_mouse.dragging && !evt.LeftIsDown() && !evt.RightIsDown() && !evt.MiddleIsDown())
+            // reset dragging state if the user released the mouse button outside the 3D scene
+            m_mouse.dragging = false;
+
 //#if defined(__WXMSW__) || defined(__linux__)
 //        // On Windows and Linux needs focus in order to catch key events
         // Set focus in order to remove it from object list
diff --git a/src/slic3r/GUI/Gizmos/GLGizmoFlatten.cpp b/src/slic3r/GUI/Gizmos/GLGizmoFlatten.cpp
index 398aebb52f..98058ee17b 100644
--- a/src/slic3r/GUI/Gizmos/GLGizmoFlatten.cpp
+++ b/src/slic3r/GUI/Gizmos/GLGizmoFlatten.cpp
@@ -60,11 +60,13 @@ void GLGizmoFlatten::data_changed(bool is_serializing)
 {
     const Selection &  selection    = m_parent.get_selection();
     const ModelObject *model_object = nullptr;
+    int                instance_id = -1;
     if (selection.is_single_full_instance() ||
         selection.is_from_single_object() ) {        
         model_object = selection.get_model()->objects[selection.get_object_idx()];
+        instance_id = selection.get_instance_idx();
     }    
-    set_flattening_data(model_object);
+    set_flattening_data(model_object, instance_id);
 }
 
 bool GLGizmoFlatten::on_init()
@@ -156,9 +158,9 @@ void GLGizmoFlatten::on_unregister_raycasters_for_picking()
     m_planes_casters.clear();
 }
 
-void GLGizmoFlatten::set_flattening_data(const ModelObject* model_object)
+void GLGizmoFlatten::set_flattening_data(const ModelObject* model_object, int instance_id)
 {
-    if (model_object != m_old_model_object) {
+    if (model_object != m_old_model_object || instance_id != m_old_instance_id) {
         m_planes.clear();
         on_unregister_raycasters_for_picking();
     }
@@ -363,6 +365,7 @@ void GLGizmoFlatten::update_planes()
     m_first_instance_scale = mo->instances.front()->get_scaling_factor();
     m_first_instance_mirror = mo->instances.front()->get_mirror();
     m_old_model_object = mo;
+    m_old_instance_id = m_c->selection_info()->get_active_instance();
 
     // And finally create respective VBOs. The polygon is convex with
     // the vertices in order, so triangulation is trivial.
diff --git a/src/slic3r/GUI/Gizmos/GLGizmoFlatten.hpp b/src/slic3r/GUI/Gizmos/GLGizmoFlatten.hpp
index 1701b76a5c..ff44fcd2d0 100644
--- a/src/slic3r/GUI/Gizmos/GLGizmoFlatten.hpp
+++ b/src/slic3r/GUI/Gizmos/GLGizmoFlatten.hpp
@@ -39,6 +39,7 @@ private:
     std::vector<std::shared_ptr<SceneRaycasterItem>> m_planes_casters;
     bool m_mouse_left_down = false; // for detection left_up of this gizmo
     const ModelObject* m_old_model_object = nullptr;
+    int                m_old_instance_id{ -1 };
 
     void update_planes();
     bool is_plane_update_necessary() const;
@@ -46,7 +47,7 @@ private:
 public:
     GLGizmoFlatten(GLCanvas3D& parent, const std::string& icon_filename, unsigned int sprite_id);
 
-    void set_flattening_data(const ModelObject* model_object);
+    void set_flattening_data(const ModelObject* model_object, int instance_id);
         
     /// <summary>
     /// Apply rotation on select plane
diff --git a/src/slic3r/GUI/Gizmos/GLGizmosCommon.hpp b/src/slic3r/GUI/Gizmos/GLGizmosCommon.hpp
index 785c660766..e0d2cdb68d 100644
--- a/src/slic3r/GUI/Gizmos/GLGizmosCommon.hpp
+++ b/src/slic3r/GUI/Gizmos/GLGizmosCommon.hpp
@@ -294,7 +294,7 @@ protected:
 
 private:
     int m_print_object_idx = -1;
-    int m_print_objects_count = 0;
+//    int m_print_objects_count = 0;
     std::unique_ptr<MeshClipper> m_supports_clipper;
     std::unique_ptr<MeshClipper> m_pad_clipper;
 };
diff --git a/src/slic3r/GUI/ImGuiWrapper.cpp b/src/slic3r/GUI/ImGuiWrapper.cpp
index 4cce6e2632..0754c35cc9 100644
--- a/src/slic3r/GUI/ImGuiWrapper.cpp
+++ b/src/slic3r/GUI/ImGuiWrapper.cpp
@@ -460,7 +460,7 @@ bool ImGuiWrapper::button(const wxString &label, const wxString& tooltip)
 
     if (!tooltip.IsEmpty() && ImGui::IsItemHovered()) {
         auto tooltip_utf8 = into_u8(tooltip);
-        ImGui::SetTooltip(tooltip_utf8.c_str());
+        ImGui::SetTooltip(tooltip_utf8.c_str(), nullptr);
     }
 
     return ret;
diff --git a/src/slic3r/GUI/Jobs/ArrangeJob.cpp b/src/slic3r/GUI/Jobs/ArrangeJob.cpp
index 8115136a57..2828fc8003 100644
--- a/src/slic3r/GUI/Jobs/ArrangeJob.cpp
+++ b/src/slic3r/GUI/Jobs/ArrangeJob.cpp
@@ -231,8 +231,10 @@ coord_t get_skirt_offset(const Plater* plater) {
     // Try to subtract the skirt from the bed shape so we don't arrange outside of it.
     if (plater->printer_technology() == ptFFF && plater->fff_print().has_skirt()) {
         const auto& print = plater->fff_print();
-        skirt_inset = print.config().skirts.value * print.skirt_flow().width() +
-                                  print.config().skirt_distance.value;
+        if (!print.objects().empty()) {
+            skirt_inset = print.config().skirts.value * print.skirt_flow().width() +
+                          print.config().skirt_distance.value;
+        }
     }
 
     return scaled(skirt_inset);
diff --git a/src/slic3r/GUI/Plater.cpp b/src/slic3r/GUI/Plater.cpp
index 5808b196d0..6adabb7d68 100644
--- a/src/slic3r/GUI/Plater.cpp
+++ b/src/slic3r/GUI/Plater.cpp
@@ -6057,7 +6057,7 @@ void Plater::remove_selected()
     p->view3D->delete_selected();
 }
 
-void Plater::increase_instances(size_t num, int obj_idx/* = -1*/)
+void Plater::increase_instances(size_t num, int obj_idx, std::optional<Selection::ObjectIdxsToInstanceIdxsMap> selection_map)
 {
     if (! can_increase_instances()) { return; }
 
@@ -6067,14 +6067,26 @@ void Plater::increase_instances(size_t num, int obj_idx/* = -1*/)
         obj_idx = p->get_selected_object_idx();
 
     if (obj_idx < 0) {
-        if (const auto obj_idxs = get_selection().get_object_idxs(); !obj_idxs.empty())
-            for (const size_t obj_id : obj_idxs)
-                increase_instances(1, int(obj_id));
+        if (const auto obj_idxs = get_selection().get_object_idxs(); !obj_idxs.empty()) {
+            // we need a copy made here because the selection changes at every call of increase_instances()
+            const Selection::ObjectIdxsToInstanceIdxsMap content = selection_map.has_value() ? *selection_map : p->get_selection().get_content();
+            for (const size_t obj_id : obj_idxs) {
+                increase_instances(1, int(obj_id), content);
+            }
+        }
         return;
     }
 
     ModelObject* model_object = p->model.objects[obj_idx];
-    const int inst_idx = p->get_selected_instance_idx();
+    int inst_idx = -1;
+    if (selection_map.has_value()) {
+        auto obj_it = selection_map->find(obj_idx);
+        if (obj_it != selection_map->end() && obj_it->second.size() == 1)
+            inst_idx = *obj_it->second.begin();
+    }
+    else
+        inst_idx = p->get_selected_instance_idx();
+
     ModelInstance* model_instance = (inst_idx >= 0) ? model_object->instances[inst_idx] : model_object->instances.back();
 
     bool was_one_instance = model_object->instances.size()==1;
diff --git a/src/slic3r/GUI/Plater.hpp b/src/slic3r/GUI/Plater.hpp
index fa2ec65080..a76ef6f1cb 100644
--- a/src/slic3r/GUI/Plater.hpp
+++ b/src/slic3r/GUI/Plater.hpp
@@ -250,7 +250,7 @@ public:
     void reset_with_confirm();
     bool delete_object_from_model(size_t obj_idx);
     void remove_selected();
-    void increase_instances(size_t num = 1, int obj_idx = -1);
+    void increase_instances(size_t num = 1, int obj_idx = -1, std::optional<Selection::ObjectIdxsToInstanceIdxsMap> selection_map = std::nullopt);
     void decrease_instances(size_t num = 1, int obj_idx = -1);
     void set_number_of_copies();
     void fill_bed_with_instances();
diff --git a/src/slic3r/GUI/SceneRaycaster.cpp b/src/slic3r/GUI/SceneRaycaster.cpp
index 1f44a07d6d..64493d86b4 100644
--- a/src/slic3r/GUI/SceneRaycaster.cpp
+++ b/src/slic3r/GUI/SceneRaycaster.cpp
@@ -117,7 +117,7 @@ SceneRaycaster::HitResult SceneRaycaster::hit(const Vec2d& mouse_pos, const Came
                 return false;
 
             if (hit.type == SceneRaycaster::EType::Volume)
-                m_selected_volume_already_found = *m_selected_volume_id == decode_id(hit.type, hit.raycaster_id);
+                m_selected_volume_already_found = *m_selected_volume_id == (unsigned int)decode_id(hit.type, hit.raycaster_id);
 
             m_closest_hit_pos = hit.position;
             return true;