QprogressDialog appears at creation with Qt5.5rc (other than in Qt5.4)

In my application I create a QProgressDialog in the main window constructor for later usage.
Then I initialize it:
m_progressDlg->setMinimum(0);
m_progressDlg->setMinimumDuration(2000);

With Qt up to 5.4 the progress dialog dows not appear on startup.
With Qt5.5rc it appears after 2 seconds. As a workaround I added the line
m_progressDlg->reset();
in the mai window constructor in order to get the same behavior as in former versions.

May be related to QTBUG-46853