QNetworkAccessManager doesn't obey QNetworkProxyFactory::setUseSystemConfiguration()

[zaphod.b]

Consider the following code fragment:

QNetworkProxyFactory::setUseSystemConfiguration(true);
 
QNetworkAccessManager manager;
QNetworkProxy::ProxyType type = manager.proxy().type();     //DefaultProxy
QNetworkProxyFactory *factory = manager.proxyFactory();     //0x0

QNetworkProxyFactory::setUseSystemConfiguration(true);

QNetworkAccessManager manager;
QNetworkProxy::ProxyType type = manager.proxy().type();     //DefaultProxy
QNetworkProxyFactory *factory = manager.proxyFactory();     //0x0

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I'd expect QNetworkAccessManager to obey the internal global QNetworkProxyFactory created by QNetworkProxyFactory::setUseSystemConfiguration(true), but it doesn't.
(Observed on Windows - don't know if that matters.)

Is this a bug or a feature? If a feature, what might be the reasoning?