Background:
On OS X 10.9 and later, when a Messages notification arrives, the notification patch has a 'Reply' button that allows you to reply right in the notification patch. The current application remains active (windowDidResignMain: is NOT called) but the key window loses key (windowDidResignKey: IS called) because the notification patch has a text input to type your response in. A native Cocoa application correctly notifies it's key NSWindow with windowDidResignKey: and calls windowDidBecomeKey: when the Messages patch is dismissed.

Description:
When the Messages notification patch 'Reply' button is clicked and the notification text input becomes key, a Qt 5.4.1 application QMainWindow that has had setFocusPolicy(Qt::StrongFocus) set on it will NOT have focusOutEvent() called on it.