QC1 Menu breaks activeFocus in QQuickWidget

When a Quick Controls 1 Menu is opened inside of a QQuickWidget, the focus will be changed to an non-existent item (0x0). It then cannot be changed back, breaking QML focus handling.

It works correctly when run inside a QQmlApplicationEngine.

I've tested Qt 5.9.5 and 5.12 Beta, and the issue is present in both.

See the attached project for a MWE. Switch focus between the rectangles by clicking on them, trigger the menu by rightclicking the first one. Afterwards, switching focus doesn't work anymore, and neither does capturing keyboard events.