As Tim replied in another thread (I think he meant to reply to this thread), some applications will seem like it is 'stalled' until you move the mouse around, then the install will continue.
I have seen this issue in my own testing and could not find the root cause of the problem, but I'm thinking it maybe due to the installer itself being launched by bddrun.
My workaround was to create an AutoIt script that launches the unattended install, then script the mouse to move every few seconds until the installation is done.
-Brian