Qt crashes after aborting a QNetworkAccessManager::put() FTP upload operation

My program does an FTP upload inside a QDialog. The user can cancel the dialog, which calls
QNetworkReply->abort() and reject() of the dialog, after which the dialog is deleted.
Still, the Qt mainloop tries to access somehow QFtpDTP::writeData() and crashes, as the accessed object
was already deleted.
See the attached valgrind logfile.
I also attach the source to the dialog implementation, with which you should be able to reproduce the problem.