I've noticed an odd incompatibility the the Wordpress SEO plugin by Yoast. When the SEO plugin is activated, clicking on the username link (http://ask.os.com/questions/user/schnallity) in a question redirects to the home page instead of the expected user page. Deactivate the SEO plugin and it works normally.
I'm using WP 3.1.2, BP 1.2.8 and the BP Community Theme. I've deactivated the SEO plugin for now, but I'd really like to figure out what's causing this.