MistyDM on "[Plugin: MP Spam Be Gone] IE 9.0 in Windows Vista?"

I've had a few readers mention that they can't comment on my site when this plugin is active. No matter how many times they check the box and try to comment, they are told that they can't comment until they check the box. Everyone with this issue has had IE 9.0 and Windows Vista. ?????

http://wordpress.org/extend/plugins/mp-spam-be-gone/