Xen users - Mar 2014 - substantial shutdown delay for PV guests with PCI -passthrough

Hi list,
I am experiencing a substantial delay if I shutdown a PV linux guest 
which has PCI devices passed-through:

I start the domain using
	xl create -c domain

Then I login from the connected console and do a
	shutdown -h now
which results in normal shutdown messages (w/o errors) showing on the 
console screen. The last line of messages then reads:
	[   36.535466] reboot: System halted

So all seems normal and as expected; the strange thing, however, is that 
the prompt in dom0 only returns after a substantial amount of time which 
appears to be _proportional_ to the number of PCI devices passed 
through: For every device specified in the
	pci = [ bb:dd.f, ... ]
entry in the guest configuration file the delay is 10 seconds. In other 
words for 4 PCI devices passed through, it takes 40 seconds before the 
prompt in dom0 returns (though I did not make any test with more than 4 
devices).

If I issue the command
	xl list
from an other terminal connected to dom0 while the delay is on-going it 
shows that the domain in question remains in the state 's', which 
according to the man page indicates that "the guest OS has shut down 
(SCHEDOP_shutdown has been called) but the domain is not dying yet". 
This state does not change until the prompt in dom0 returns (at least 
repeated 'xl list' commands show the same output) and then the line for 
the domain is gone.

If no devices are passed through, the prompt in dom0 after having shut 
down the domU appears without any noticeable delay.

All tests have been performed using the same environment while only 
changing the relevant line in the domU configuration file.

The xen version used is 4.3.1-r5, xen-tools is also 4.3.1-r5 and the 
kernel used for both dom0 and domUs is 3.11.7 (hardende gentoo sources).

The system is capable of vt-d and uses a Xeon E3-1260L processor.

Do these observations ring a bell with anybody or is this even expected 
behaviour. If this is not normal - which I would expect as I have not 
been able to find any information relating to substantial delays during 
shutdown - how would I go about getting to the grounds of this?

Thanks and regards Atom2