BuddyPress.org

If removing those lines fixes the problem for you, I would say remove those lines.

Those are settings that need to be modified to correctly for your particular install. WordPress and bbPress will often times suggest those settings for you, but it may not have gotten them correct.

I think I understand what you’re saying, and honestly it doesn’t resonate in my mind how this could happen unless your cookie settings are mucked up. WordPress and BuddyPress use the same login and logout functions, they are performing the exact same tasks.

Try deleting all of the cookies for your particular site, and try logging in/out again.

Have you attempted to integrate bbPress or have you modified your cookie settings in any way?