Hello Dave,
Please keep in mind that this is the expected behavior. The "PrepareDlg" is shown for a little amount of time, as its description states:
Please wait while the Setup Wizard prepares to guide you through the installation
After the "preparations" are done (few actions are executed), the "WelcomeDlg" dialog is spawned.
Just let us know if you have any other questions.
All the best,
Catalin