I’m resurrecting this because I have the same issue.
The odd thing is that, if I click on either the item image or the “Item” link, it opens in the same page and respects the page layout setting. Clicking on the item name, however, opens in a new tab and immediately changes the item layout to full width, causing any sidebars to drop down below the item area.
It’s this new tab behaviour which isn’t respecting the theme default layout.
If I can simply stop the item name link opening in a new tab, I’m pretty sure it will solve the problem.