Comment 3 for bug 220656

This looks like an old report, but I ran into the same type of issue.

I do not have a solution, but an ugly hack to test if zenity is running and if not kill the children processes.

That statement just looks wrong o.O

At any rate ...

Take a command foo ...

foo | zenity --progress --auto-kill & # Need to add an & at the end so the script continues.
RUNNING=0
while [ $RUNNING - eq 0 ]
do
 if [ -z "$(pidof zenity)" ] ; then
    pkill foo # You may need to kill -9 `pidof foo`
    RUNNING=1
fi
done

NOTE : this just kills the children precesses, you may also want to clean up after them (remove temp files ...)