[Plugin: MailChimp List Subscribe Form] Groups selection doesn't work

I have a plugin setup to a list with groups. It shows up and everything seems nice and dandy. But when you sign up for a specific group, you sign up to the list but for some reason you don’t sign up for that group you’ve picked. Even email confirmation shows groups field as blank.

I’ve contacted customer support (Bob), he was able to duplicate the problem and advised to post here to figure out why groups don’t work in this plugin.

dev.viktorix.com/blog
you’ll see plugin in sidebar.