Unexpected changes are made to the main asset when cloning and adding root objects with AddObjectToAsset in AssetPostprocessor

How to reproduce:
1. Open the attached "IN-141614_3299215 - SubAssetBug.zip" project
2. In the Project tab, right click on the "Brick_3020" asset
3. Press "Reimport"
4. Observe the Console

Actual result: Console logs "[FbxSubAssetProcessor] Main asset at 'Assets/Brick_3020.fbx': name='Brick_3020', type=DummyAsset"
Expected result: Console logs "[FbxSubAssetProcessor] Main asset at 'Assets/Brick_3020.fbx': name='Brick_3020', type=UnityEngine.GameObject"

Reproducible with: 2023.1.0a1, 6000.0.74f1, 6000.3.15f1, 6000.4.6f1, 6000.5.0b7, 6000.6.0a4

Reproducible on: Windows 11
Not reproducible on: No other environments tested

Notes:

• The script excecuted in this project is located in "Editor/FbxSubAssetProcessor.cs". If the section of it where the root object is cloned is removed (lines 11-17), we see the expected output.
• If the section adding DummyAsset scriptable objects to the asset is removed (Lines 19-26), The output is still not expected but the type given is Material rather than DummyAsset:
  "[FbxSubAssetProcessor] Main asset at 'Assets/Brick_3020.fbx': name='Brick_3020', type=UnityEngine.Material"