freebsd stable - Sep 2006 - RELENG_6 power button ignored after halt if ACPI enabled

I've just upgraded 2 machines to 6.2-PRERELEASE #1: Sat Sep 16 18:31:43 
NZST 2006:

- Supermicro P3TDER (Serverworks HE-SL Chipset, AMIBOIS)
- Supermicro P3TDDE (VIA Apolla 266 chipset, AWARD)

They both exhibit the same problem:

If ACPI is enabled, shutting down via 'shutdown -h' appears to work 
properly (judging by the console output) - however to actually power off 
the machine the power button must be held until the power supply detects 
that the button has been down for 20s and turns us off.

Poweroff via 'shutdown -p' and reboot via 'shutdown -r' all work
ok.

If I boot with ACPI disabled, then after 'shutdown -h', pressing the 
power button works in the usual way (i.e powers off after about 1-2 
seconds).

Given that the two machines are reasonably different, this looks like it 
might be common - anyone else seeing this?

In terms of getting more information to help debug this, what is the 
best way to proceed?

Cheers

Mark

Oops - didn't know about the -acpi mailing list, will post there, sorry.

Mark