Regression in qmlRegisterType

It's not possible to use qmlRegisterType<QQuickWindow>() anymore. Now it fails with the following error:

In file included from /home/kde-devel/kde5/include/QtQml/qqml.h:37:0,
from /home/kde-devel/kde5/include/QtQuick/qquickwindow.h:42,
from /home/kde-devel/kde5/include/QtQuick/qquickview.h:37,
from /home/kde-devel/kde5/include/QtQuick/QQuickView:1,
from /home/kde-devel/tmp/bgtest/main.cpp:3:
/home/kde-devel/kde5/include/QtQml/qqmlprivate.h: In instantiation of ‘static QObject* QQmlPrivate::AttachedPropertySelector<T, 1>::attachedProperties(QObject*) [with T = QQuickWindow]’:
/home/kde-devel/kde5/include/QtQml/qqmlprivate.h:180:20: required from ‘static QObject* (* QQmlPrivate::AttachedPropertySelector<T, 1>::func())(QObject*) [with T = QQuickWindow; QQmlAttachedPropertiesFunc = QObject* (*)(QObject*)]’
/home/kde-devel/kde5/include/QtQml/qqmlprivate.h:190:130: required from ‘QObject* (* QQmlPrivate::attachedPropertiesFunc())(QObject*) [with T = QQuickWindow; QQmlAttachedPropertiesFunc = QObject* (*)(QObject*)]’
/home/kde-devel/kde5/include/QtQml/qqml.h:113:48: required from ‘int qmlRegisterType() [with T = QQuickWindow]’
/home/kde-devel/tmp/bgtest/main.cpp:24:35: required from here
/home/kde-devel/kde5/include/QtQml/qqmlprivate.h:172:48: error: cannot convert ‘QQuickWindowAttached*’ to ‘QObject*’ in return
return T::qmlAttachedProperties(obj);
^
/home/kde-devel/kde5/include/QtQml/qqmlprivate.h: In instantiation of ‘static const QMetaObject* QQmlPrivate::AttachedPropertySelector<T, 1>::attachedPropertiesMetaObject(ReturnType* (QObject*)) [with ReturnType = QQuickWindowAttached; T = QQuickWindow]’:
/home/kde-devel/kde5/include/QtQml/qqmlprivate.h:183:74: required from ‘static const QMetaObject* QQmlPrivate::AttachedPropertySelector<T, 1>::metaObject() [with T = QQuickWindow]’
/home/kde-devel/kde5/include/QtQml/qqmlprivate.h:196:136: required from ‘const QMetaObject* QQmlPrivate::attachedPropertiesMetaObject() [with T = QQuickWindow]’
/home/kde-devel/kde5/include/QtQml/qqml.h:114:54: required from ‘int qmlRegisterType() [with T = QQuickWindow]’
/home/kde-devel/tmp/bgtest/main.cpp:24:35: required from here
/home/kde-devel/kde5/include/QtQml/qqmlprivate.h:176:20: error: incomplete type ‘QQuickWindowAttached’ used in nested name specifier
return &ReturnType::staticMetaObject;