MFMailComposeViewController shown over UITabBarController

I have to fix the following issue:

A MFMailComposeViewController is shown over an UITabBarController. When pressing Cancel on the mail composer view, the action sheet ap开发者_如何学Pythonpears. Since the mail composer is shown over the tab controller, the tab controller blocks the surface of the Cancel button here. Only the upper part can receive the push (the black bar behind the action sheet's lower part is the tab bar). You can find a screenshot here: http://i.imgur.com/RsCYm.png

Any ideas how to fix this? Thanks!