In my generated .chm file, when I'm in a file in one of the
books and click a link that takes me to another book within that
same .chm file, my original book automatically collapses. This
doesn't happen in all of my projects, though - is there a setting
to make it so no matter where I am, the books in my table of
contents stay expanded unless I click the Expand/Collapse
There are a bunch of settings that govern the way the TOC
behaves. To edit them, look at your Single Source Layouts area.
Right-click the layout you wish to modify (in your case, Microsoft
HTML Help). See that button named
Edit just to the right of the Advanced Settings? Click it
and you should see a dialog named HTML Help - Advanced Settings.
You should now see a tab labeled "TOC Styles". Click that tab. The
option that causes the open books to collapse when opening a
different book is named
Single Click to Open Books. DE-select that option and
dismiss all the dialogs. Re-compile and you should then be set.