The QTIFW crashes in the PerformInstallationForm on the windows-platform when the installer-window loses the focus before changing to PerformInstallationPage. The reason is a missing check for a NULL-pointer around line 190 in performinstallationform.cpp:

#ifdef Q_OS_WIN
if (m_taskButton)

{ if (!m_taskButton->window()) m_taskButton->setWindow(QApplication::activeWindow()->windowHandle()); m_taskButton->progress()->setValue(progressPercentage); }

#endif

should be:

#ifdef Q_OS_WIN
if (m_taskButton)

{ if (!m_taskButton->window() && QApplication::activeWindow()) m_taskButton->setWindow(QApplication::activeWindow()->windowHandle()); m_taskButton->progress()->setValue(progressPercentage); }

#endif

A patch is attached too.