Bug Overriding Canvas-Inspector does not show Nested Inspector when calling base

I'm trying to override the Inspector for the Canvas-Component, so that I can add some buttons to quickly set the Sorting-Order based on 'layers' I've created within my Game.
(Canvas-based UI doesn't use Sorting Layers, so I've resorted to setting up my own 'layers' based on sorting order).

However.. Whenever I override the Inspector for the Canvas, and call either

base.OnInspectorGUI()

or

DrawDefaultInspector()

I am NOT getting the proper inspector for nested Canvas-Components.
Instead, I get an Inspector showing the Canvas as being in WorldSpace, not showing the 'sortingOrder' at all.


Regular Inspector for nested Canvas:


When Overridden:


Is there any way for me to have the engine render the correct Inspector for nested Canvases?


Full script (have to cast target for setting order because they're properties with InternalCall-attributes) :

Code (CSharp):

1. [CustomEditor(typeof(Canvas))]
2.     public class CanvasEditor : UnityEditor.Editor
3.     {
4.         public const int BACKGROUND_LAYER = -7_500;
5.         public const int MIDGROUND_LAYER = 1_000;
6.         public const int FOREGROUND_LAYER = 7_500;
7.  
8.         public override void OnInspectorGUI()
9.         {
10.             serializedObject.Update();
11.             Canvas cv = (Canvas)target;
12.             if (!cv.isRootCanvas) // Sorting Order not shown on Root Canvas
13.             {
14.                 if (GUILayout.Button(new GUIContent("Move to Background")))
15.                     SetOrder(BACKGROUND_LAYER);
16.                 if (GUILayout.Button(new GUIContent("Move to MidGround")))
17.                     SetOrder(MIDGROUND_LAYER);
18.                 if (GUILayout.Button("Move to ForeGround"))
19.                     SetOrder(FOREGROUND_LAYER);
20.                 GUILayout.Space(10f);
21.                 if (GUILayout.Button(new GUIContent("Move Forward 5")))
22.                     SetOrder(cv.sortingOrder + 5);
23.                 if (GUILayout.Button(new GUIContent("Move Backward 5")))
24.                     SetOrder(cv.sortingOrder - 5);
25.                 GUILayout.Space(15f);
26.             }
27.             DrawDefaultInspector();
28.         }
29.  
30.         private void SetOrder(int order)
31.         {
32.             serializedObject.Update();
33.             Canvas cv = (Canvas)target;
34.             cv.overrideSorting = true;
35.             cv.sortingOrder = order;
36.             EditorUtility.SetDirty(cv);
37.         }
38.     }