Copy and Paste sometimes don't appear in my UITextView

I created an app with a UITextView and occasionally it won't show the Select, Copy, Paste menu items when I tap on text. If I double-tap the home button and close the开发者_JS百科 app, then re-open it, I'm able to do it again, which makes me think it's a memory problem (if it doesn't have enough memory, it doesn't show the menu?)

The problem in my case is that I created a UIWindow to cover the main window. I gave that window a windowLevel of UIWindowLevelAlertView / 20, so that it would hover between the main window and alert views. However, occasionally, AlertViews upon releasing key window, would revert the key window to my cover, and not the main window, and that would invalidate the menu controller's ability to properly display itself over the UITextView that was sitting in the main window.