Undo in Editor only executed when I switch focus to Hierarchy

I am currently trying to write a custom editor that uses drag and drop. I have managed to get it running by setting the controlID. Unfortunately, when I do this Undo only works when I switch focus away from the Scene. The weirdest thing is that while it does nothing the menu item for Undo still highlights. Am I somehow using the controlID in a wrong way, or do I need to forward the keyboard controls somehow?

I have built a minimal example, that has the problem. I add a behavior to a simple Game Object like a cube:

 public class CubeBehavior : MonoBehaviour {
 
     public int value = 0;
 
 }

Next I create a custom editor that increases the value with every mouse click. I also register this change for undo. It works, but only once I set focus outside of the Scene.

 using UnityEngine;
 using System.Collections;
 using UnityEditor;
 
 [CustomEditor (typeof(CubeBehavior))]
 public class CubeEditor : Editor {
 
     CubeBehavior cubeBehavior;
 
     void OnEnable() {
         cubeBehavior = (CubeBehavior)target;
         SceneView.onSceneGUIDelegate -= OnScene;
         SceneView.onSceneGUIDelegate += OnScene;
     }
 
     public override void OnInspectorGUI() {
         EditorGUILayout.BeginHorizontal();
         cubeBehavior.value = EditorGUILayout.IntField (cubeBehavior.value);
         EditorGUILayout.EndHorizontal();
     }
 
     void OnScene(SceneView sceneview) {
         Event e = Event.current;
         
         int controlID = GUIUtility.GetControlID (FocusType.Passive);
         EventType eventType = e.GetTypeForControl (controlID);
         
         Ray r = Camera.current.ScreenPointToRay(new Vector3(e.mousePosition.x, -e.mousePosition.y + Camera.current.pixelHeight));
         Vector3 mousePos = r.origin;
         
         if (eventType == EventType.MouseUp) {
             Undo.RegisterUndo (target, "Edit " + target);
             Undo.IncrementCurrentGroup ();
             ((CubeBehavior) target).value ++;
             GUIUtility.hotControl = controlID;
             e.Use ();
         }
     }
 
 }