Prefab modification is not detected when adding a new array element

2023.1.X

As Designed

Note that you need to use RecordPrefabInstancePropertyModifications() when editing properties directly instead of using SerializedProperty. Check the docs for for an example: https://docs.unity3d.com/ScriptReference/PrefabUtility.RecordPrefabInstancePropertyModifications.html [CustomEditor(typeof(NewBehaviourScript))] public class NewBehaviourScriptEditor : Editor { public override void OnInspectorGUI() { base.OnInspectorGUI(); if (GUILayout.Button("Change Data")) { var target = (NewBehaviourScript)this.target; Undo.RecordObject(target, "Change Data"); target.data = new float[] { 0, 1, 2, 3, 4, 9999, 5, 6, 7, 8, 9 }; PrefabUtility.RecordPrefabInstancePropertyModifications(target); // <--- you need this } } }