Okay, with 1.0-a-5 trunk I get the same old inactive user when I register via WP. No errors on the page or in the log, though.
Also I got this error, which I fixed by flipping back to the old file:
Call to undefined function wp_check_invalid_utf8() in
/home/XX/public_html/forums/bb-includes/functions.wp-core.php on line 60