Displaying heading text in a book

[Doug]

I use Frame 7.0p579 on WinXP.

The index of my book uses a 2-column body text frame labeled A.  The
index heading sports an overhead line, and since we want this to span
the width of the page, we have placed the heading in a separate text
frame, tagged IX.  The problem is that in the book, when I toggle it
to Display Heading Text, the index displays the capital letter A and
not the word Index from the heading.

Both text frames, A and IX, feature the Autoconnect checkbox checked. 
If I clear the checkbox from the A text frame and save the file, the
entry in the book file changes from A to the filename.fm, even though
the rest of the books shows heading text and not filenames.

My question is:  what logic does Frame use to decide which text to
display in the book when the Display Heading Text mode is selected? 
In blank empty test books I've tried, it takes the first text entered
in the A text frame.  I've tried swapping name tags of the two text
frames but this doesn't help.

--Doug