On an Android QML application, when focus has been moved to the QML UI by clicking anywhere in the UI, the native Android back-key does not work for the first time. Same happens if an Android activity is opened from the application. After first press the key starts working and events go to the application.

The first case can be easily reproduced with a default Qt QML application in Qt Creator. Create it, deploy to Android device. Back-key works if user does not tap on the UI. But if it is tapped, first back-key press does not work.