libvirt users - Jan 2012 - Should Windows NT guest use all of a CPU?

I've "ported" an old VMware VM containing Windows NT 4 SP6 into
libvirt/kvm/qemu and got it running (more or less).

However, the CPU graph next to the VM in virt-manager shows it
starts using 100% of the allocated CPU as soon as it reaches
the "OS Loader" screen, and stays there even after Windows has
booted and I've logged in.  (There's a dip now and then, apparently
when something other than idling happens!)

Windows NT Task Manager shows the CPU usage at 0%.

I've tried with and without ACPI, and with different CPU settings
(none/default, qemu32, pentium).  No difference.

Host is running Fedora 16 x86_64 with the latest updates:
gpxe-roms-qemu-1.0.1-4.fc16.noarch
qemu-kvm-0.15.1-3.fc16.x86_64
qemu-system-x86-0.15.1-3.fc16.x86_64
qemu-common-0.15.1-3.fc16.x86_64
qemu-img-0.15.1-3.fc16.x86_64
libvirt-0.9.6-4.fc16.x86_64
libvirt-client-0.9.6-4.fc16.x86_64
libvirt-python-0.9.6-4.fc16.x86_64
virt-manager-common-0.9.0-7.fc16.noarch
virt-manager-0.9.0-7.fc16.noarch

No other VM (Linux or Windows) behaves this way.
I thought NT was deemed to be "well behaved"
(e.g., uses HLT instruction), so I'm wondering
if this is normal.

ps shows (except for bits I've hidden):

/usr/bin/qemu-kvm -S -M pc-0.14 -cpu qemu32 -enable-kvm -m 384 -smp
1,sockets=1,cores=1,threads=1 -name BPrjwtest -uuid <hidden>
-nodefconfig -nodefaults -chardev
socket,id=charmonitor,path=/var/lib/libvirt/qemu/BPrjwtest.monitor,server,nowait
-mon chardev=charmonitor,id=monitor,mode=control -rtc base=localtime
-device lsi,id=scsi0,bus=pci.0,addr=0x6 -drive
file=/home/libvirt/images/BPrjwtest.img,if=none,id=drive-ide0-0-0,format=raw
-device ide-drive,bus=ide.0,unit=0,drive=drive-ide0-0-0,id=ide0-0-0,bootindex=1
-drive
file=<hidden>,if=none,media=cdrom,id=drive-ide0-1-0,readonly=on,format=raw
-device ide-drive,bus=ide.1,unit=0,drive=drive-ide0-1-0,id=ide0-1-0,bootindex=2
-netdev tap,fd=30,id=hostnet0 -device
ne2k_pci,netdev=hostnet0,id=net0,mac=<hidden>,bus=pci.0,addr=0x4
-chardev pty,id=charserial0 -device
isa-serial,chardev=charserial0,id=serial0 -usb -device
usb-tablet,id=input0 -vnc 127.0.0.1:3 -vga vmware -device
AC97,id=sound0,bus=pci.0,addr=0x5 -device
virtio-balloon-pci,id=balloon0,bus=pci.0,addr=0x3