Tags to keep top-of-mind not working as expected

I started with just an @todo tag. All was well.
Then I added an @projects tag and used Customize to add @projects to the list of tags to keep in mind. I got a separate @projects entry on my daily digest, exactly as I expected and wanted.
Then I added another tag, @errands, and added this tag to the list of tags to keep in mind. This broke the categorization of the daily digest - the @todo, @projects, and @errands items all appeared under To-Dos, instead of in three separate lists in the digest.
So far, I have not found a way to fix this.