Reliability of open_port's exit_status option

[Holger Weiß]

The documentation on erlang:open_port/2 says:  "If the port program
closes its stdout without exiting, the exit_status option will not
work."  What exactly does that mean?  Is the manual simply telling me
that the status won't be reported before the port process actually
exited (which seems a little too obvious) or is there anything else that
could happen (such as the status not being reported even if the port
process eventually exits)?

Holger