Mac installer command hangs on 10.5/10.6 but not 10.4

What would cause the Mac installer command to hang when installing an app from a shell script? The last output the installer gets to is "Preparing开发者_JAVA技巧 Target Volume". This behavior is observed on 10.5 and 10.6 but not 10.4.

You can use Activity Monitor to take a Sample (stack trace) or a hung process and see where it's stuck.

I've been getting this hanging behavior on my installs. Quitting the iphone simulator fixes mine.