Would your colleagues happen to using either the "index.html" or "start.html" files to open your prototype's generated HTML output? For the locally generated HTML, the sidebar will appear depending on which file is opened: opening the index.html or start.html files will launch the prototype's home page with the sidebar open, while opening one of the page's HTML files directly (e.g. "page_1.html" for a page titled "Page 1") will launch that page with the sidebar closed.
Clicking "Generate" in the Generate HTML dialog will automatically open the HTML file corresponding to the selections in the "Open With" section in the browser, however the generated files themselves won't be affected by those selections. If your colleagues would like to view the generated HTML without the sidebar, they'll want to launch the prototype by opening one of the page's HTML files directly (or the "start_c_1.html" file, which will open it with the sidebar minimized).
Hopefully this helps clarify some things! Please let me know if you have any questions about this.