CustomEditor Inheritance Issue

Hi, I have a class that derives from UnityEngine.UI.Button
And my CustomEditor class derives from UnityEditor.UI.ButtonEditor.

My problem is that when I call ApplyModifiedProperties() all my custom variables are saved while the standard button variables are lost.
I've noticed that if I DON'T call ApplyModifiedProperties() all standard variables are saved while mine are lost.

 [CustomEditor(typeof(CustomButton), true)]
 public class CustomButton_Editor : ButtonEditor
 {
     private SerializedObject m_Object;
     private SerializedProperty m_Property;
         
     protected override void OnEnable()
     {
         m_Object = new SerializedObject(target);
         base.OnEnable();
     }
 
     public override void OnInspectorGUI()
     {
         ...
         ...
         m_Property = m_Object.FindProperty("_scaleTo");
         EditorGUILayout.PropertyField(m_Property, new GUIContent(m_Property.displayName, m_Property.tooltip));
 
         base.OnInspectorGUI();
 
         m_Property = m_Object.FindProperty("_triggerDirectly");
         EditorGUILayout.PropertyField(m_Property, new GUIContent(m_Property.displayName, m_Property.tooltip));
 
         if (GUI.changed)
         {
             m_Object.ApplyModifiedProperties();
         }
     }
 }

I'm using Unity version: 5.3.3p1

So does anyone have any idea how to solve this?
Thank you.