iOS6：MFMailComposeViewController加载缓慢，闪烁黑屏; MailCompositionS开始占用内存

On iOS 6, after sending a few email messages (by using MFMailComposeViewController), the email screens become very slow to open- at first opening with none of the fields populated (no Subject, no body, etc.) for a few seconds, and eventually (after sending about 8 messages), a black screen is displayed to the user for a few seconds before the email view controller is properly displayed. On iOS 6, after sending a few email messages (b