I was using the old Simple Tags p[lugin previously, one where you put
[tag]tag1[/tag] around text in your post that you wanted to make a tag and
[tags]tag2[/tags] at the bottom of the post with tag2 being text not found in the post.
This new Simple Tags plugin is supposed (or at least that's what I gather) to import the old tags but it doesn't. Now in all my old posts that have those old tags in them the words that are tagged no longer show up when the posts are viewed.