I’m also using your plugin (thanks for it! it’s really great) and was having the same problem. I just fixed it here and I don’t think there’s anything wrong with the plugin.
In my case, I am using a custom theme based on blankslate. In that theme’s horrifically, atrociously, abhorrently formatted functions.php there was this function:
add_filter('wp_title', 'blankslate_filter_wp_title');
function blankslate_filter_wp_title($title)
{
return $title . esc_attr(get_bloginfo('name'));
}
I just deleted that, and that solved it. So I would suggest searching your theme files for “wp_title”, and see if there’s a filter like this. If so, delete it, and that should do it.