Custom editor, not serializing

I have this code:

 using UnityEngine;
 #if UNITY_EDITOR
 using UnityEditor;
 #endif
 using System.Collections.Generic;
 
 
 public class PrefabEditor : MonoBehaviour
 {
     #if EDITOR_FROM_SCRIPT
     [HideInInspector] public bool showOriginalFields = false;
     [SerializeField, HideInInspector] private int _selectedCat = 0;
     [SerializeField] private bool _showCat = true;
     [SerializeField] private string _output = "Prefab save path";
     [SerializeField] private string _prefabName = "New prefab name";
     [SerializeField] private List<Object> _category = new List<Object>();
 
     public int selectedCat
     {
         get{return _selectedCat;}
         set{_selectedCat = value;}
     }
 
     public string[] CategoryName
     {
         get
         {
             // init array
             string[] result = new string[_category.Count];
             // set the array
             for(int i = 0; i < _category.Count; i++)
             {
                 if(null == _category[i]) continue;
 
                 result[i] = _category[i].name;
             }
             // return it
             return result;
         }
     }
 
     public bool CategoryEmpty
     {
         get{return null == _category || (null != _category && 0 == _category.Count);}
     }
 
 #if UNITY_EDITOR
     public void Inspector_Draw()
     {
         // Draw toggle
         if(IEditor.Button(showOriginalFields ? "Hide [orignal fields]" : "Show [orginal fields]"))
             showOriginalFields = !showOriginalFields;
         // Draw header
         Inspector_Header();
     }
 
     private void Add()
     {
         // Add an empty object
         _category.Add(null);
     }
 
     private void Clear()
     {
         // Prompt the user
         bool confirm = EditorUtility.DisplayDialog("Prefab Editor", "Are you sure you want to delete all categories", "Yes", "No");
         // exit if confirmation was negative
         if(!confirm) return;
         // clear category list
         _category.Clear();
     }
 
     public void Inspector_Header()
     {
         EditorGUILayout.BeginVertical("Box");
         {
             // The output dictionary
             IEditor.Label("Prefab", EditorStyles.boldLabel);
 
             // [indent]++
             EditorGUI.indentLevel++;
             {
                 _output = EditorGUILayout.TextField("Output", _output);
                 _prefabName = EditorGUILayout.TextField("Name", _prefabName);
             }
             EditorGUI.indentLevel--;
             
             // [Space]
             EditorGUILayout.Space();
             
             // Label categories
             IEditor.Label("Categories", EditorStyles.boldLabel);
 
             EditorGUILayout.BeginHorizontal();
             {
                 if(IEditor.Button("Add", EditorStyles.miniButtonLeft))
                     Add();
 
                 if(_category.Count == 0)
                 {
                     if(IEditor.Button(_showCat ? "Hide" : "Show", EditorStyles.miniButtonRight))
                         _showCat = !_showCat;
                 }
                 else
                 {
                     if(IEditor.Button(_showCat ? "Hide" : "Show", EditorStyles.miniButtonMid))
                         _showCat = !_showCat;
 
                     if(IEditor.Button("Delete", EditorStyles.miniButtonRight)) Clear();
                 }
             }
             EditorGUILayout.EndHorizontal();
 
             // Debug.LogFormat("CatEmpty {0}", CategoryEmpty);
 
             // exit if item has nothing
             if(!CategoryEmpty)
             {
                 // Draw the categories
                 Inspector_DrawCategory();
 
                 if(_selectedCat > 0 && _selectedCat < _category.Count - 1)
                 {
                     // Draw the selection grid
                     Inspector_SelectionGrid();
                 }
             }
         }
         EditorGUILayout.EndVertical();
     }
 
     private void Inspector_DrawCategory()
     {
 
         if(_showCat)
         {
             // [Space]
             EditorGUILayout.Space();
             // [HelpBox] Tip
             IEditor.Box("Drag and drop folder as new category", IEditor.ExpandWidth);
 
             EditorGUILayout.BeginVertical("Box");
             {
                 EditorGUILayout.Space();
 
                 // Draw items
                 for(int i = 0; i < _category.Count; i++)
                 {
                     EditorGUILayout.BeginHorizontal();
                     {
                         _category[i] = EditorGUILayout.ObjectField(i + " Category", _category[i], typeof(Object), true) as Object;
                         
                         if(IEditor.Button("Delete", EditorStyles.miniButtonRight, IEditor.DontExpandWidth))
                         {
                             _category.RemoveAt(i);
                             continue;
                         }
                     }
                     EditorGUILayout.EndHorizontal();
                 }
             }
             EditorGUILayout.EndVertical();
         }
     }
 
     private void Inspector_SelectionGrid()
     {
         if(null != _category[_selectedCat]) return;
         // [Space]
         EditorGUILayout.Space();
 
         EditorGUILayout.BeginHorizontal("Box");
         {
             GUILayout.Label("Selected");
             selectedCat = GUILayout.SelectionGrid(selectedCat, CategoryName, 5, EditorStyles.miniButton);
         }
         EditorGUILayout.EndHorizontal();
     }
     #endif
 }

And this one:

 using UnityEngine;
 using UnityEditor;
 using System.Collections;
 
 [CustomEditor(typeof(PrefabEditor))]
 public class IPreabEditor : Editor
 {
     private PrefabEditor I
     {
         get{return target as PrefabEditor;}
     }

     public override void OnInspectorGUI ()
     {
         if(I.showOriginalFields) base.OnInspectorGUI ();
 
         I.Inspector_Draw();
     }
 }

Unity won't detect any changes if I hit the add button on the inspector, thoughts?