virt-manager doesn't report the kvm guest OS information with a message 'Not connected'.

Issue

We attempted to shut down several kvm guest OSes on virt-manager.  When we
clicked the shutdown button to some kvm guest OS, virt-manager didn't report
the kvm guest OS information with a message "Not connected".

Step to Reproduce:
1. Install several kvm guest OSes.
2. Start up those OSes.
3. Shut down those OS in series.
<Please retry step 2-3 until this problem is reproduced.>

Actual Results:
virt-manager doesn't report the kvm guest OS information with a message
"Not connected".

Expected Results:
virt-manager reports the kvm guest OS information anytime without a message
"Not connected".