This is a documented bug. But I think it's so severe that it should still be considered a bug. It falls into the category "Qt doesn't support Qt".

Place main.qml, Button1.qml and Button2.qml in the same folder, run qmlscene.

You see a gray window, blue rectangle and while/yellow circle button. Press the button. Observe the log output.

Now close qmlscene, edit main.qml, and flip the `bug: ` boolean property.

Rerun the example. click the button. Look at console output. The example shows that buttons not directly using MouseArea don't work with composed event propagation.

The drag feature of MouseArea only works for MouseArea. You can't have a RoundButton under it.

I hope I'm wrong. But this cast seems to be quite central:

   QQuickMouseArea* ma = qobject_cast<QQuickMouseArea*>(item); 
    if (ma && ma != q && ma->isEnabled() && itemPrivate->acceptedMouseButtons() & ev->button()) { 
        switch (sig) {