The following crashes when attempting to convert 'a' to a QVariantMap (infinite loop).

import QtQuick 2.0

Rectangle {
    width: 360
    height: 360

    Component.onCompleted: {
        var a = {}
        var b = {}

        a.c = b;
        b.c = a;
        return a;
    }
}

While this isn't the correct fix for this issue, it might also be worth bypassing this particular conversion for signals, as the return value can't be used?