*Something* is going wrong. The most likely candidate is ACPI, as every hardware vendor's implementation is a little bit different, and none seem to follow the ACPI specification.
You could try disabling ACPI, before starting up the kernel:
At the boot> prompt, type: boot -c
At the first UKC> prompt, type: disable acpi
At the next UKC> prompt, type: quit
The kernel will boot without ACPI; it will use APM if available from your BIOS.
If the system comes up, you can make the change permanent:
# config -euf /bsd
Then type quit at the first UKC> prompt.