operation-->system-->permissions-->admin-->moderator

when we test admin, after you click 'Action' dropdown button, if your module content over one screen, then you scroll the scrollbar ,you will see the dropdown menu will cover the module fixed navigation.
![component](https://f.cloud.github.com/assets/3860758/566176/c92a1236-c673-11e2-99d0-99c181187ae7.png)