Description of problem:
Boot a guest with virtio balloon device, and balloon the memory to a smaller one.
Then hot plug the second virtio balloon device, the memory value will be re-set to the original value as configured in the qemu command line. Then balloon the memory, it works well.

Version-Release number of selected component (if applicable):
kernel-2.6.32-171.el6.x86_64
qemu-kvm-0.12.1.2-2.171.el6.x86_64

How reproducible:
Always

Steps to Reproduce:
1.Boot guest with one virtio balloon device.
/usr/libexec/qemu-kvm -m 16G -smp 4 -cpu cpu64-rhel6,+x2apic -usbdevice tablet -drive file=win7-64-virtio.qcow2,format=qcow2,if=none,id=drive-ide0-0-0,werror=stop,rerror=stop,cache=none -device virtio-blk-pci,drive=drive-ide0-0-0,id=ide0-0-0 -netdev tap,id=hostnet0,script=/etc/qemu-ifup -device e1000,netdev=hostnet0,mac=00:10:1a:20:06:28,bus=pci.0,addr=0x6 -boot dc -uuid bea9c85e-0a47-4030-979d-5d94bb3d6161 -rtc-td-hack -no-kvm-pit-reinjection -monitor stdio -qmp tcp:0:4444,server,nowait -name win7-64-balloon -spice disable-ticketing,port=5931 -vga qxl -device virtio-balloon-pci,bus=pci.0,id=balloon0

2.Balloon the memory, it works.
{"execute":"query-balloon"}
{"return": {"actual": 17179869184}}


{"execute":"balloon","arguments":{"value":16106127360}}
{"return": {}}

{"execute":"query-balloon"}
{"return": {"actual": 16106127360}}

3.Hot plug another virtio balloon device.
{"execute":"device_add","arguments":{"driver":"virtio-balloon-pci","id":"balloon1"}}
{"return": {}}

4. Check the memory:
{"execute":"query-balloon"}
{"return": {"actual": 17179869184}}

5. 
{"execute":"balloon","arguments":{"value":16106127360}}
{"return": {}}

{"execute":"query-balloon"}
{"return": {"actual": 16743661568}}

  
Actual results:
After step4, the memory value is re-set to the original max value.

Expected results:
After step4, the memory value should not change.

Additional info: