Description of problem:

virtio ballon driver crash (blue screenà on Windows server 2008 R2 standard (1.118 unstable or latest stable same problem).
Works ok with v1.81

Steps to Reproduce:
1. Install 1.81
2. Upgrade to 1.118 using iso file

Actual results:
Blue screen

Expected results:
No blue screen

Additional info:
virtualization host: proxmox/qemu 

proxmox-ve-2.6.32: 3.4-177 (running kernel: 2.6.32-46-pve)
pve-manager: 3.4-14 (running version: 3.4-14/793d1699)
pve-kernel-2.6.32-37-pve: 2.6.32-150
pve-kernel-2.6.32-22-pve: 2.6.32-107
pve-kernel-2.6.32-46-pve: 2.6.32-177
pve-kernel-2.6.32-26-pve: 2.6.32-114
lvm2: 2.02.98-pve4
clvm: 2.02.98-pve4
corosync-pve: 1.4.7-1
openais-pve: 1.1.4-3
libqb0: 0.11.1-2
redhat-cluster-pve: 3.2.0-2
resource-agents-pve: 3.9.2-4
fence-agents-pve: 4.0.10-3
pve-cluster: 3.0-20
qemu-server: 3.4-9
pve-firmware: 1.1-5
libpve-common-perl: 3.0-26
libpve-access-control: 3.0-16
libpve-storage-perl: 3.0-35
pve-libspice-server1: 0.12.4-3
vncterm: 1.1-8
vzctl: 4.0-1pve6
vzprocps: 2.0.11-2
vzquota: 3.1-2
pve-qemu-kvm: 2.2-25
ksm-control-daemon: 1.1-1
glusterfs-client: 3.5.2-1