Machine does not shutdown with certain configuration

[Edward Macfarlane Smith]

Since getting my new laptop (Sony PCG-Z1SP, it's a Centrino machine) I had 
never got it to successfully power off. I had just been using the SuSE kernel 
and then the same configuration that worked well on a couple of other 
machines, but I then tried a different configuration and it powered off, 
after I did a little playing I tracked it down to the "Local APIC support on 
uniprocessors" option. Turning this off makes the machine poweroff. 
I have checked this on 2.4.21-rc6-ac1 and 2.4.21-ac1. I just thought other 
people might find that useful to know. 
The text on the help for CONFIG_X86_UP_APIC seems to suggest it's fine to use 
it on any machine (and certainly while running it seems to make no 
difference), would a patch to the text to indicate it may prevent power off 
be accepted, or is this problem too specific to this machine to be included?
Regards,
Edward

e.g.

--- linux-2.4.21_ac1_orig/Documentation/Configure.help  2003-06-14 
16:00:30.000000000 +0100
+++ linux/Documentation/Configure.help  2003-06-14 18:04:18.000000000 +0100
@@ -289,6 +289,8 @@
   have a local APIC, then the kernel will still run with no slowdown at
   all. The local APIC supports CPU-generated self-interrupts (timer,
   performance counters), and the NMI watchdog which detects hard lockups.
+  On some machines (e.g. Sony Vaio PCG-Z1SP) this option may prevent the
+  machine from powering off when it is halted.

   If you have a system with several CPUs, you do not need to say Y
   here: the local APIC will be used automatically.