Left-side-bar Layout

I’ve placed the [bbp-forum-index] code into a page that uses a left-side-bar template.
The content wrapper div for the forum has a class .left-layout.
But when I navigate to the topic list or further to a topic, the page layout changes to full-width where the content wrapper div now has a class full-layout.

How can I keep the left-side-bar layout throughout?

thanks!