In admin, I click on the Media menu. The submenus are Library, Add New, and Media-Tags.
When I click on the Media-Tags submenu, it takes me to the right page. But in the left navigation bar, the "current menu" is now Posts, and it shows the Posts submenus, not the Media submenus.
It didn't happen before Media-Tags 3.0. It is happening in WP 3.1.3 and also in a site running WP 3.0.1. I'm not using any other media-related plugins on these sites.
This is not serious, just a nuisance. :)