libvirt users - Mar 2016 - changing clock on host temporarily blocks guest OS operation

I have the following running on my system:
    - one linux host running libvirt 1.2.20
    - two Linux guestOS VMs running

When I change the clock on the host, the VMs stop responding: The VNC
connection stops working, the console connection to the VMs does not work,
ping stops reponding, libvirt commands temporarily stop working (after
issuing the command, the system just hangs).

I get control back after 5 min or so, but I have to restart the VMs for
everything to work again.

Any ideas what's causing this?
Is this a know bug? Is there a fix for it?

Thanks in advance,
Andrei

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