Test this bug in RHEL7 host, components:

# uname -r
3.10.0-33.el7.x86_64
# rpm -q qemu-kvm
qemu-kvm-1.5.3-8.el7.x86_64


start cli w/ qmp:
<qemu-kvm cli> ... -qmp tcp:0:4555,server,nowait

hit same issue in RHEL7, the error is just like this:

{ "execute": "memsave",
             "arguments": { "val": 10,
                            "size": 100,
                            "filename": "/lll/lsl" } } 
{"error": {"class": "GenericError", "desc": "Could not open '/lll/lsl'"}}

{ "execute": "transaction",
     "arguments": { "actions": [
         { 'type': 'blockdev-snapshot-sync', 'data' : { "device": "drive-virtio-disk0","snapshot-file": "/some/place/my-image","format": "qcow2" } },{ 'type': 'blockdev-snapshot-sync', 'data' : { "device": "ide1-cd0","snapshot-file": "/some/place/my-image2","mode": "existing","format": "qcow2" } } ] } }
{"error": {"class": "DeviceNotFound", "desc": "Device 'drive-virtio-disk0' not found"}}

{ "execute": "change",
             "arguments": { "device": "ide1-cd0",
              "target": "/home/a"}}
{"error": {"class": "GenericError", "desc": "Could not open '/home/a'"}}


so cloned this bug