Calling typeof(x) on current object's property x during object creation causes assert failure

import QtQuick 2.5
import QtQuick.Window 2.2

Window {
	visible: true

	property var someProp
	Component.onCompleted: console.log("typeof someProp:", typeof(someProp));
}

 	msvcr120d.dll!_CrtDbgReportW(int nRptType, const wchar_t * szFile, int nLine, const wchar_t * szModule, const wchar_t * szFormat, ...) Line 279	C++
>	Qt5Cored.dll!qt_message_fatal(QtMsgType __formal, const QMessageLogContext & context, const QString & message) Line 1599	C++
 	Qt5Cored.dll!QMessageLogger::fatal(const char * msg, ...) Line 784	C++
 	Qt5Cored.dll!qt_assert(const char * assertion, const char * file, int line) Line 3045	C++
 	Qt5Qmld.dll!QV4::RuntimeHelpers::convertToObject(QV4::ExecutionEngine * engine, const QV4::Value & value) Line 440	C++
 	Qt5Qmld.dll!QV4::Value::toObject(QV4::ExecutionEngine * e) Line 305	C++
 	Qt5Qmld.dll!QV4::Runtime::typeofMember(QV4::ExecutionEngine * engine, const QV4::Value & base, int nameIndex) Line 1153	C++
 	Qt5Qmld.dll!QV4::Moth::VME::run(QV4::ExecutionEngine * engine, const unsigned char * code) Line 688	C++
 	Qt5Qmld.dll!QV4::Moth::VME::exec(QV4::ExecutionEngine * engine, const unsigned char * code) Line 960	C++
 	Qt5Qmld.dll!QV4::SimpleScriptFunction::call(const QV4::Managed * that, QV4::CallData * callData) Line 580	C++
 	Qt5Qmld.dll!QV4::Object::call(QV4::CallData * d) Line 310	C++
 	Qt5Qmld.dll!QQmlJavaScriptExpression::evaluate(QV4::CallData * callData, bool * isUndefined) Line 189	C++
 	Qt5Qmld.dll!QQmlBoundSignalExpression::evaluate(void * * a) Line 239	C++
 	Qt5Qmld.dll!QQmlBoundSignal_callback(QQmlNotifierEndpoint * e, void * * a) Line 333	C++
 	Qt5Qmld.dll!QQmlNotifier::emitNotify(QQmlNotifierEndpoint * endpoint, void * * a) Line 96	C++
 	Qt5Qmld.dll!QQmlData::signalEmitted(QAbstractDeclarativeData * __formal, QObject * object, int index, void * * a) Line 774	C++
 	Qt5Cored.dll!QMetaObject::activate(QObject * sender, int signalOffset, int local_signal_index, void * * argv) Line 3622	C++
 	Qt5Cored.dll!QMetaObject::activate(QObject * sender, const QMetaObject * m, int local_signal_index, void * * argv) Line 3600	C++
 	Qt5Qmld.dll!QQmlComponentAttached::completed() Line 136	C++
 	Qt5Qmld.dll!QQmlObjectCreator::finalize(QQmlInstantiationInterrupt & interrupt) Line 1216	C++
 	Qt5Qmld.dll!QQmlComponentPrivate::complete(QQmlEnginePrivate * enginePriv, QQmlComponentPrivate::ConstructionState * state) Line 914	C++
 	Qt5Qmld.dll!QQmlComponentPrivate::completeCreate() Line 951	C++
 	Qt5Qmld.dll!QQmlComponent::completeCreate() Line 942	C++
 	Qt5Qmld.dll!QQmlComponent::create(QQmlContext * context) Line 775	C++
 	qmlscene.exe!main(int argc, char * * argv) Line 566	C++
 	qmlscene.exe!__tmainCRTStartup() Line 626	C
 	qmlscene.exe!mainCRTStartup() Line 466	C
 	kernel32.dll!BaseThreadInitThunk()	Unknown
 	ntdll.dll!RtlUserThreadStart()	Unknown

Heap::Object *RuntimeHelpers::convertToObject(ExecutionEngine *engine, const Value &value)
{
    Q_ASSERT(!value.isObject());
    switch (value.type()) {
    case Value::Undefined_Type:
    case Value::Null_Type:
        engine->throwTypeError();
        return 0;
    case Value::Boolean_Type:
        return engine->newBooleanObject(value.booleanValue());
    case Value::Managed_Type:
        Q_ASSERT(value.isString());
        return engine->newStringObject(value.stringValue());
    case Value::Integer_Type:
    default: // double
        return engine->newNumberObject(value.asDouble());
    }
}