[Plugin: Bad Behavior] Comment errors

Since upgrading to Bad Behavior 2.0.21 I get error messages when trying to comment a post (see below). However, the comment appears when I return to the post and refresh it. I don’t have any cache plugins activated. Any ideas?

Warning: Wrong parameter count for array_key_exists() in /***/html/wp-content/plugins/bad-behavior/bad-behavior/post.inc.php on line 33

Warning: Cannot modify header information – headers already sent by (output started at /***/html/wp-content/plugins/bad-behavior/bad-behavior/post.inc.php:33) in /***/html/wp-content/plugins/bad-behavior/bad-behavior/screener.inc.php on line 8

Warning: Cannot modify header information – headers already sent by (output started at /***/html/wp-content/plugins/bad-behavior/bad-behavior/post.inc.php:33) in /***/html/wp-includes/pluggable.php on line 770