Supporter - Plugins menu still visibile to none supporters

We've installed the supporter plugin as per install text and everything seems to be hunky dory except our "non supporters" can still see the Plugin's tab in their admin main menu.

The supporter_plugins.php is in the mu-plugins dir as per install. Now we were using Plugin Commander, and before we removed it we made sure that everything was disabled and plugins deactivated in the commander menu, so I'm wondering if there's something elsewhere that's causing this.

Any suggestions please.. thank you!