I can't turn off a VM via "Virtual Machine Manager". As I click on either "Shut Down" or "Force  Off" the virtual console closes, but the domain is still listed as running in the main window. OTOH, here's what `xm list' and `xl list' think about that (domain name is Debian-HVM):

# xm list
Name                                        ID   Mem VCPUs      State   Time(s)
Debian-HVM                                      2048     2                 0.0
Domain-0

# xl list
Name                                        ID   Mem VCPUs	State	Time(s)
Domain-0

Also, any subsequent attempt of rebooting, pausing or starting again the same domain fails.
  
Here's what VMM says:

Error shutting down domain: failed Xen syscall  ioctl 3166208

Traceback (most recent call last):
  File "/usr/share/virt-manager/virtManager/asyncjob.py", line 44, in cb_wrapper
    callback(asyncjob, *args, **kwargs)
  File "/usr/share/virt-manager/virtManager/asyncjob.py", line 65, in tmpcb
    callback(*args, **kwargs)
  File "/usr/share/virt-manager/virtManager/domain.py", line 1094, in destroy
    self._backend.destroy()
  File "/usr/lib64/python2.7/site-packages/libvirt.py", line 553, in destroy
    if ret == -1: raise libvirtError ('virDomainDestroy() failed', dom=self)
libvirtError: failed Xen syscall  ioctl 3166208

Here's the info about versions of xen* and libvirt* related packages:
# rpm -qa | grep xen
xen-4.1.1-6.fc16.x86_64
netxen-firmware-4.0.534-4.fc15.noarch
xen-libs-4.1.1-6.fc16.x86_64
xen-hypervisor-4.1.1-6.fc16.x86_64
xen-runtime-4.1.1-6.fc16.x86_64
xen-doc-4.1.1-6.fc16.x86_64
xen-licenses-4.1.1-6.fc16.x86_64

# rpm -qa | grep libvirt
libvirt-client-0.9.6-2.fc16.x86_64
libvirt-python-0.9.6-2.fc16.x86_64
libvirt-0.9.6-2.fc16.x86_64