How to fix navigation button activity in Responsive HTML5 output through FM2017?

When I click next/previous button it navigates to next file available in book instead of Headings. My headings are properly ordered in TOC and it looks like this:

As you can see the screenshot the 'Heading 1 again' topic is in the same file and next Heading 1 are separate files. So when I click next button, it skips the topic 'Heading 1 again'.

I was searching some way through Style mapping option but couldn't fix.