Clearing cache is not possible with QNetWorkAccessManager

If QNetworkAccessManager is used to get data from our ftp server it works good if the urls are valid but the moment one url is invalid(file does not exist on the ftp server)the following request with valide url fails and shows the error.

A small example application is attached:
Press the button "Send Request 1" to get the data from "ftp://ftp.qt.nokia.com/copyrightnotice.txt". The data will be displayed in the corresponding textbox,
Next press the "Send Request 2" button and an error occurs because the file does not exist.
Now press the "Send Request 1" button again there is the same error like in the previous request.

In Qt5 we have a method QNetworkAccessManager::clearAccessCache()which does the clearing of cache but in Qt4 there is no public method, there is one QNetworkAccessManagerPrivate::clearCache()but this is for auto test.