To reproduce, change the example page.html and wrap the entire contents of the body in the following tags:

<div style="height:500px; width:700px; overflow:auto;">

man page here

</div>

You will see that it is barely possible to go back/forward by swiping to the left/right when the mouse is in the content area even though there is no horizontal scroll bar.

It seems like the scrollWheel callback in DHSwipeClipView is not called often enough in this case.