Wow, I wish I had known this earlier or I would not have installed bbpress.
I have three s2member roles ‘UK Member, UK Student, International Member’, which means I would have to make everyone in one of those groups a moderator 🙁
Back to the drawing board…
Did you ever get to the bottom of this? I seem to be having the same problem. Looking at the HTML source, I do not see the wp-content/themes/mytheme/css/bbpress.css file being included at all.