We have tested with both Dutch and French keyboards, and found that only a QEvent::KeyRelease event is received without a QEvent::KeyPress preceding it. This is when a custom event handler is installed using installEventFilter(). The following dead keys are known to have this issue:

Qt::Key_Dead_Tilde
Qt::Key_Dead_Circumflex
Qt::Key_Dead_Diaeresis
Qt::Key_Dead_Grave
Qt::Key_Dead_Acute
Qt::Key_Dead_Cedilla

I've also attached code which can be used to demonstrate the issue with an international keyboard (such as French or Dutch). The output will only show key releases, and that no key press events are received by the handler.