Scripted sysinstall fails with "Command 'system' failed"

[PeterSteele]

I'm building a sysinstall script and everything is working except a final post install script that I want to run. According to the docs I can do this using the system command. For example:

command=/stand/post_install.sh
system

However, the script fails to run, with sysinstall giving the error

Command 'system' failed - rest of script aborted."

I've tried other commands as tests, and nothing seems to work--they all give this error.

I know the script works because if I jump into the live shell and run the script manually, there are no complaints. Is there some trick needed to run a command through the install.cfg file during a scripted sysinstall?