HTML5 shows filenames when used with groups/folders in book

Just talked to support and was told that it is expected that when your book includes folders or groups, the files underneath the groups will be shown in the HTML5 output in the TOC as filenames, not the heading/title inside the file. So for example, if you would have in a normal TOC:

Getting Started

What Is This Nifty Product?

Installing Our Nifty Product

In HTML5 you get in the contents pane:

Getting Started

what_is_nifty

install_nifty

Adobe support in its infinite wisdom suggested I change my filenames; not an option for me sadly.

Does anyone else know a workaround? Thanks!!