@rmarcus

you can use kill to kill a process
ps -a
kill (number of a process)

to see all processes, than select one you want to kill (close),
watch processes tree for subprocesses

btw

did you try the following shell commands
(shell commands generally don't change with OS, GUI, as there are very basic Linux/ Debian shell commands)

If you can't run them, install another shell - bash
and try to run them again
and attach terminal screenshots.

As N900 is a phone, mayby there is one another process run,
to keep phone functionality on, protecting phone
against internal interferring with calls on hold, sms and the like.

In my case (Nokia 770)
I have installed bash shell 3.2
I can run bash from CLI

~ $ bash
bash-3.2$

bash-3.2$ shutdown 1 -h
( no need for sudo gainroot)

rebooted after 1 min (the above)

============
=======================================

$ sudo gainroot

/home/user # shutdown 1 -h

shutdown 1
shut down and reboot after 1 min

shutdown 1 -hP

shut down and powered off