AssetPostprocessor, AssetImporter set spritePackingTag invalid, Can't change texture meta.

i use AssetPostprocessor AssetImporter like this: inherit AssetPostprocessor, and use OnPostprocessAllAssets funtion.

 private static void PresetUITexture(AssetImporter assetImporter, string atlasName, string assetName)
 {
     TextureImporter textureImporter = (TextureImporter)assetImporter;
     if (textureImporter == null) 
    {
         return;
     }

     textureImporter.mipmapEnabled = false;
     textureImporter.spritePackingTag = atlasName;

     textureImporter.textureFormat = TextureImporterFormat.AutomaticCompressed;
 }

i use reimport option to reimport my textures. e.g: i want set the packing tag "UI_ITEM" to my all textures. it will work in unity editor, i can see the packing tag changed in editor window.

But i find the texture meta not changed.
before: after:

So if i close unity editor at now, texture import settings will be rest. the packing tag "UI_ITEM" will be lost....

Then i found, if i reimport all texures twice. texture metas will be changed in the second reimport .