Problems rebooting/ACPI problem with HT in RC2

In 5.3 Beta7, RC1, and RC2 I've been having a problem with ACPI on a 
system I'm building.

When I try to reboot the system or to do a shutdown -p with SMP and ACPI 
enabled as soon as it gets to  "Shutting down ACPI" it crashes and fills 
part of the screen with garbage characters.

If I select APCI disabled at the boot screen it will be able to reboot 
and shutdown/powerdown just fine, but then again SMP obviously doesn't 
work either. The generic kernel in Beta7 and RC1 which had SMP enabled 
by default did this as well, so I dont think its the result of anything 
in my customer kernels. If ACPI is enabled but SMP is not, it will also 
reboot fine so I'm pretty sure this is a SMP/Hyperthreading issue but it 
is definitely a show stopper for me. I dont have any other systems which 
are multi-processor or hyperthreading enabled to test to see if it's 
specific to my hardware though.

In RC1 (I think I had KDB, DDB, WITNESS, and INVARIANTS enabled in the 
kernel for this one) this shows up in /var/log/messages:

Oct 31 12:47:55 synapscape kernel: Shutting down ACPI
Oct 31 12:47:55 synapscape kernel: ke
Oct 31 12:47:55 synapscape kernel: <18446744072652783764>kkernel trap 1 
with interrupts disabled
Oct 31 12:47:55 synapscape kernel:
Oct 31 12:47:55 synapscape kernel:
Oct 31 12:47:55 synapscape kernel: Fatal trap 1: privileged instruction 
fault while in kernel mode
Oct 31 12:47:55 synapscape kernel: cpuid = 0; apic id = 00
Oct 31 12:47:55 synapscape kernel: instruction pointer  = 0x8:0xc2c32003
Oct 31 12:47:55 synapscape kernel: stack pointer                = 
0x10:0xeb41c777
Oct 31 12:47:55 synapscape kernel: frame pointer                = 
0x10:0xeb41c838
Oct 31 12:47:55 synapscape kernel: code segment         = base 0x0, 
limit 0xfffff, type 0x1b
Oct 31 12:47:55 synapscape kernel: = DPL 0, pres 1, def32 1, gran 1
Oct 31 12:47:55 synapscape kernel: processor eflags     = resume, IOPL = 0
Oct 31 12:47:55 synapscape kernel: current process              = 37 
(swi5: clock sio)
Oct 31 12:47:55 synapscape kernel: trap number          = 1
Oct 31 12:47:55 synapscape kernel: panic: privileged instruction fault
Oct 31 12:47:55 synapscape kernel: cpuid = 0
Oct 31 12:47:55 synapscape kernel: boot() called on cpu#0

In RC2 this shows up in /var/log/messages:

Oct 31 15:44:04 synapscape kernel: Shutting down ACPI
Oct 31 15:44:04 synapscape kernel: <kernel trap 12 with interrupts disabled
Oct 31 15:44:04 synapscape kernel:
Oct 31 15:44:04 synapscape kernel:
Oct 31 15:44:04 synapscape kernel: Fatal trap 12: page fault while in 
kernkernel trap 12 wkietrhn eiln tterrarpu pts1 2d iwsiatbhl eidnt
Oct 31 15:44:04 synapscape kernel: er
Oct 31 15:44:04 synapscape kernel: r
Oct 31 15:44:04 synapscape kernel: uFpattsa ld itsraabpl ed