I am so sorry for this and cannot rebuild this behavior yet...
I've tested this whole bbPress thing A LOT BEFORE release and always worked!
I just tested with Lifestyle 2.0 and your prefered layout and also worked!
Question: do you have any other layout setting in your functions.php regarding the forum?
You could try a re-save of the regular Genesis layout option and ALSO in the plugin's page: set the forum on "Genesis Default" and then save. Then re-open the plugin's page and select "Content-Sidebar" and save. -- Does that help?
Did you before use version 1.0 of the plugin maybe? Or do you have any other layout options set with hooks or other plugins? (Could be a priority conflict...)
Hope this helps a bit :)