inconsistent TextureImporter settings

i'm experiencing some inconsistencies between projects using the same code (an editor script to create textures) & assets.

the following code creates a TextureImporterSettings with various settings.

     var importSettings =  new TextureImporterSettings
         {
             npotScale = TextureImporterNPOTScale.None,
             readable = true,
             mipmapEnabled = false,
             wrapMode = TextureWrapMode.Clamp,
             filterMode = FilterMode.Point,
             maxTextureSize = 1024,
             textureFormat = TextureImporterFormat.AutomaticTruecolor
         };

     importSettings.ApplyTextureType(TextureImporterType.Advanced, true);

then i'm applying them to an asset that i've created using:

             if (savedFilename != "")
             {
                 AssetDatabase.Refresh();

                 var importer = AssetImporter.GetAtPath(savedFilename) as TextureImporter;

                 if (importer != null)
                 {
                     importer.SetTextureSettings(importSettings);
                     AssetDatabase.WriteImportSettingsIfDirty(savedFilename);
                 }
              }

this is only applied to successfully created textures.

inconsistencies arise when i copy the editor script that this code is from to a different project. in one, the texture is (correctly) shown with a type of 'Advanced' but, in another, the type is 'Sprite 2D \ uGUI'.

my only assumption is that by creating importSettings, is that they will be dirty, and therefore written.

any suggestions as to why this might be happening?

thanks in advance.