Description of problem:
QE tested qemu-kvm-rhev-1.5.3-60.el7ev, it hit the same issue as 1114793 bug. so file a new bug to track this issue. I am trying to reproduce it with qmp command directly.  will update result to bz asap.

Version-Release number of selected component (if applicable):
qemu-kvm-rhev-1.5.3-60.el7ev.x86_64
3.10.0-123.4.2.el7.x86_64

How reproducible:
100%

Steps to Reproduce:
1.qemu-img create -f raw base.img 10M

2.qemu-img create -f qcow2 -b base.img -o backing_fmt=raw snap1.img

3.qemu-img create -f qcow2 -b snap1.img -o backing_fmt=qcow2 snap2.img
# set up blank space to hold the copy
touch copy.img
# cp base.img copy.img 

4.xml file
<domain type='kvm'>
 <name>testvm4</name>
 <memory unit='MiB'>256</memory>
 <vcpu>1</vcpu>
<os>
<type arch='x86_64' machine='pc-i440fx-rhel7.0.0'>hvm</type>
<boot dev='hd'/>
</os>
 <devices>
   <disk type='file' device='disk'>
     <driver name='qemu' type='qcow2' cache='none'/>
     <source file='/var/lib/libvirt/images/snap2.img'/>
     <target dev='hda' bus='virtio'/>
   </disk>
   <graphics type='vnc'/>
 </devices>
</domain>

5.# check for events
virsh event testvm1 block-job --loop --timeout 10 &
pid=$!
sleep 1
# run the blockcopy
virsh blockcopy testvm1 vda --wait --verbose --raw /tmp/copy.img --reuse-external
echo job started
sleep 5
virsh blockjob testvm1 vda --abort
wait $pid

Actual results:
error: Requested operation is not valid: domain is not transient

job started
error: Requested operation is not valid: No active operation on device: drive-virtio-disk0

Expected results:

Block Copy: [  0 %]event 'block-job' for domain testvm1: Block Copy for /tmp/snap2.img ready
Block Copy: [100 %]
Now in mirroring phase
job started
event 'block-job' for domain testvm1: Block Copy for /tmp/snap2.img completed

event loop timed out
events received: 2

Additional info: