bbPress is a forum software which, in the older versions worked as a “standalone” forum and in some ways it had some degree of integration with WordPress forums, but not fully integrated. The latest versions of this software work as a WordPress plugin, having all functionality inside WordPress database and structure.
This is not one of my favorite forum software, and not one of my choice (mainly because there are a lot of functionality like emoticons, private messages, and other common forum tools that are not included, and for which we will need to download extra plugins to use those) but sometimes we need to take an existing bbPress forum and update it to the latest version of WordPress.
There are a few problems that show up when trying to migrate the forum data from an older version of bbPress (standalone versions) lower than the bbPress 1.2 version, in which case a few steps must be done for updating it, because an upgrade to the 1.2 version must be done manually.