I ran into that exact same problem; no matter what you changed the user role into, he/she would always stay a member. bbPress would also NOT give me the “profile updated” message after submit.
My guess: since I was also using a localised version of WP (I had already tried to just include WP, not use the wp_ tables for user info), a lot of strings were translated, including the roles. It even changed the URL to the profile edit page to /profile/2/bewerken/ (bewerken == edit).
And sure enough, after complete removing the WP inclusion code, things worked again…
Maybe there’s some strings being gettext’d, that shouldn’t be?
