[Wayland] Menu behaviour erratic (disappears too easily)

When running an application with main window menus (e.g., creator or examples/widgets/mainwindows/application/application), menus disappear far too easily.

On the QWindow compositor example, they flash on and disappear.

On Weston, they flash when used for the first time. Then they appear to work, but do disappear when a submenu is shown.

On the terminal, it says:

This plugin does not support raise()
This plugin does not support grabbing the keyboard