Description of problem:
Each time after implement the "guest-get-vcpus" command, the guest agent is not available any more. The commands could not be executed successfully unless restart the qemu-ga service inside guest (or kill "qemu-ga" daemon and re-do "qemu-ga -d").

Version-Release number of selected component (if applicable):
Host:
kernel-2.6.32-429.el6.x86_64
qemu-kvm-0.12.1.2-2.415.el6.x86_64

Guest:
qemu-guest-agent-0.12.1.2-2.415.el6.x86_64

How reproducible:
Always

Steps to Reproduce:
1. Boot a guest with virtio-serial:

# /usr/libexec/qemu-kvm -M rhel6.5.0 -cpu SandyBridge -m 2G -smp 2,sockets=1,cores=2,threads=1,maxcpus=16 -enable-kvm -name win7-32 -uuid 990ea161-6b67-47b2-b803-19fb01d30d12 -smbios type=1,manufacturer='Red Hat',product='RHEV Hypervisor',version=el6,serial=koTUXQrb,uuid=feebc8fd-f8b0-4e75-abc3-e63fcdb67170 -k en-us -rtc base=localtime,clock=host,driftfix=slew -nodefaults -monitor stdio -qmp tcp:0:6666,server,nowait -boot menu=on  -global PIIX4_PM.disable_s3=0 -global PIIX4_PM.disable_s4=0 -monitor unix:/tmp/monitor-unix,nowait,server -drive file=/home/RHEL6.5-64.qcow2,if=none,id=drive-virtio-disk0,format=qcow2,cache=none,werror=stop,rerror=stop,aio=threads -device virtio-blk-pci,scsi=off,bus=pci.0,drive=drive-virtio-disk0,id=virtio-disk0 -netdev tap,id=hostnet0,vhost=on -device virtio-net-pci,netdev=hostnet0,id=net0,mac=00:1a:4a:2e:28:1c,bus=pci.0,addr=0x4 -vga std -vnc :10 -usb -device usb-tablet -chardev socket,path=/tmp/qga.sock,server,nowait,id=qga0 -device virtio-serial -device virtserialport,chardev=qga0,name=org.qemu.guest_agent.0

2. Install qemu-guest-agent package inside guest and start qemu-ga service.

3. Execute some qemu-ga commands:
{"execute":"guest-ping"}
{"return": {}}  ===> Succeed

3.
{"execute":"guest-get-vcpus"}
{"return": [{"online": true, "can-offline": false, "logical-id": 0}, {"online": true, "can-offline": true, "logical-id": 1}]}

======> Succeed here.

4. Repeat step 3 again:

{"execute":"guest-get-vcpus"}

======> No response.

5. {"execute":"guest-ping"} ===> No response

6. Restart qemu-ga service inside guest
{"execute":"guest-ping"}
{"return": {}}

======> Work again.


Actual results:
Each time after implement "guest-get-vcpus" guest agent command, the guest agent will not work any more unless restart the qemu-ga inside guest. 

Expected results:
Guest agent should always work. 

Additional info: