Periodicals transfer as "Books"
In another thread, noticed someone having this problem with Kindle Touch also, but the partial workaround suggested there doesn't seem to work with Fire.
Basically, all news/periodical files transferred from calibre to Fire, either via USB or Email, show up OK as .mobi files. But they are all rendered as Books, i.e. they have no navigational controls (e.g., sections/article lists, etc). Just as with a book, you can "Go To . . ." the Table of Contents and navigate to a single article, but would have to repeat that procedure for each article.
Will send request to Amazon to look into the issue. Suggest others might do the same. Or some maybe some genius can figure out a fix. This behavior renders any kind of use of Calibre's "news" feature with the Kindle Fire (or the Touch) pretty useless.