It's hard to say what it was but one thing that helps when editing Styles and Folder Formats is to always close the lister and open a new one after making some changes. Then you can see the effect things will have in a clean context, where no settings are cached.
See the folder formats FAQ (linked in my sig) for info about the way formats can be cached for a particular lister. It can be quite confusing if you don't know about it.
Edit 2019: If you want a button that toggles Flat View and filters out all files (keeping folders) at once: