Use of signal connect prevents efficient function lookup

On a project using the QML Compiler, connecting a custom signal to a function, anonymous or named results in a warning on the block where the connection is taking place, for being unable to generate efficient code for the lookup of function property.

The following example can be copy-pasted into a main.qml to re-produce the issue:

> Warning: Main.qml:4:18: Could not compile binding for onCompleted: Cannot generate efficient code for lookup of function property. [compiler]
>         qtobject.mySignal.connect( () => { } );
>                  ^^^^^^^^

import QtQuick
Window {
    Component.onCompleted: {
        qtobject.mySignal.connect( () => { } );
    }
    QtObject {
        id: qtobject
        signal mySignal()
    }
}