implemented a std::deque to handle the insert order:

This ensures, that both selected and inserted elements are inserted in the correct order.
Selected elements are handled as stack to emplace them to the old position.
New elements are pushed back now.

src/control/tools/EditSelectionContents.cpp

@@ -61,8 +61,13 @@ EditSelectionContents::~EditSelectionContents() {
  * Add an element to the this selection
  */
 void EditSelectionContents::addElement(Element* e, Layer::ElementIndex order) {
+    g_assert(this->selected.size() == this->insertOrder.size());
     this->selected.emplace_back(e);
-    this->indexWithinLayer.emplace(e, order);
+    if (order == Layer::InvalidElementIndex) {
+        this->insertOrder.emplace_back(e, order);
+    } else {
+        this->insertOrder.emplace_front(e, order);
+    }
 }
 
 /**
@@ -271,6 +276,7 @@ void EditSelectionContents::fillUndoItem(DeleteUndoAction* undo) {
     }
 
     this->selected.clear();
+    this->insertOrder.clear();
 }
 
 /**
@@ -328,10 +334,8 @@ void EditSelectionContents::finalizeSelection(double x, double y, double width,
 
     bool move = mx != 0 || my != 0;
 
-
-    for (auto it = this->selected.rbegin(); it != this->selected.rend(); ++it) {
-        Element* e = *it;
-
+    g_assert(this->selected.size() == this->insertOrder.size());
+    for (auto&& [e, index]: this->insertOrder) {
         if (move) {
             e->move(mx, my);
         }
@@ -341,14 +345,11 @@ void EditSelectionContents::finalizeSelection(double x, double y, double width,
         if (rotate) {
             e->rotate(x, y, this->lastWidth / 2, this->lastHeight / 2, this->rotation);
         }
-
-        auto layerIndex = indexWithinLayer.find(e);
-        if (layerIndex == indexWithinLayer.end() ||
-            layerIndex->second ==
-                    Layer::InvalidElementIndex) {  // if the element didn't have a source layer (e.g, clipboard)
+        if (index == Layer::InvalidElementIndex) {
+            // if the element didn't have a source layer (e.g, clipboard)
             layer->addElement(e);
         } else {
-            layer->insertElement(e, layerIndex->second);
+            layer->insertElement(e, index);
         }
     }
 }

src/control/tools/EditSelectionContents.h

@@ -11,8 +11,8 @@
 
 #pragma once
 
-#include <map>
-#include <string>
+#include <deque>
+#include <utility>
 #include <vector>
 
 #include "control/Tool.h"
@@ -175,12 +175,13 @@ class EditSelectionContents: public ElementContainer, public Serializeable {
     /**
      * The selected element (the only one which are handled by this instance)
      */
-    vector<Element*> selected;
+    std::vector<Element*> selected;
 
     /**
      * Mapping of elements in the selection to the indexes from the original selection layer.
+     * Defines a insert order over the selection.
      */
-    std::map<Element*, Layer::ElementIndex> indexWithinLayer;
+    std::deque<std::pair<Element*, Layer::ElementIndex>> insertOrder;
 
     /**
      * The rendered elements