Hey guys,
As a theme developper I wanted to bring bbPress support and I was facing the same issue.
The plugin that @robin-w brought was working but I know something was wrong with my theme.
I managed to make it work without the plugin by deleting this snippet from functions.php :
https://codex.wordpress.org/Plugin_API/Action_Reference/pre_get_posts#Exclude_Pages_from_Search_Results
The intent of this snippet is to exclude pages from search results and I guess this was conflicting with WP4.
If you have this problem with your theme, look for “pre_get_posts” actions and if the search query is updated.
Hope that can helps 🙂
