I've been seeing this 'ExpandAll' button on my HTML5 Help toolbar, and it appears to do absolutely nothing and will only draw complaints from users. I've tried it in all browsers and my side menus don't open and close like I imagined they would.
I've simply had to get rid of the button by removing it via the 'Toolbar Buttons' panel that is opened by selecting the 'Toolbar' option in the skin's editor. It seems a shame, though, as it might have been a useful option.