After update from 2.4 to 3.1 the network of the vm is running nuts

[RMM]

hello

This night I updated from proxmox 2.4 to 3.1 using the updatig script.
everything worked fine so far...
also the virtualmachine start up correctly and everything, but the networking just isn't working properly, I've never seen something like that before.
Inside the two virtual macines, the network is working, I can conect to the internet and other machines on the network.
But I can't connect from one virtual machine to the other, no other machine on the network can connect to one of the two virtual machines (not even ping it).
Also the proxmox host can't ping them, at least not really. That's where it starts getting strange.
As soon as I start one of the virtual machines, it doesn't matter which one, even the one which doesn't have this ip adress, I can ping
192.168.1.2
Even when the operating system (windows) isn't loaded yet.
From everywhere on the network I can ping this IP-Adress then, but I can't access any services. As I said, I can even ping it, when the started virtual machine doesn't have this ip address.
With arp -a it shows me that the ip address is related to the correct mac address (the mac address of the virtual machine with this ip address).
Even if I stop all virtual machines I still can ping this ip address...
only a restart of the server makes the ip-address disappear, until I start up one of the virtual machine (doesn't matter which one) again.
The networking of the proxmox host still works perfectly...
In proxmox 2.4 everything worked perfectly.
I checked everything I could think of, I just run out of ideas.... completly...
if anybody could give me a hint I'd be really gratefull.

I tried downgrading to 3.0, didn't help anything, still the same behaviour, some config info:

pveversion -v
pve-manager: 3.0-20 (pve-manager/3.0/0428106c)
running kernel: 2.6.32-20-pve
pve-kernel-2.6.32-20-pve: 2.6.32-100
pve-kernel-2.6.32-16-pve: 2.6.32-82
pve-kernel-2.6.32-19-pve: 2.6.32-96
lvm2: 2.02.98-pve4
clvm: 2.02.98-pve4
corosync-pve: 1.4.5-1
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: 4.0.0-1
pve-cluster: 3.0-7
qemu-server: 3.0-12
pve-firmware: 1.0-23
libpve-common-perl: 3.0-6
libpve-access-control: 3.0-6
libpve-storage-perl: 3.0-10
vncterm: 1.1-4
vzctl: 4.0-1pve3
vzprocps: 2.0.11-2
vzquota: 3.1-2

cat /etc/network/interfaces
# network interface settings
auto lo
iface lo inet loopback

iface eth0 inet manual

iface eth1 inet manual

auto bond0
iface bond0 inet manual
slaves eth0 eth1
bond_miimon 100
bond_mode active-backup

auto vmbr0
iface vmbr0 inet static
address 192.168.1.200
netmask 255.255.255.0
gateway 192.168.1.10
bridge_ports bond0
bridge_stp off
bridge_fd 0

qm config 100
boot: c
bootdisk: ide0
cores: 4
ide0: local:100/vm-100-disk-1.raw,format=raw,size=320G
ide1: local:100/vm-100-disk-3.qcow2,format=qcow2,size=32G
ide2: local:iso/virtio-win-0.1-52.iso,media=cdrom,size=57126K
memory: 16000
name: 2008SQLSERVER
net1: virtio=5E:FF:3E:CF:3A:8F,bridge=vmbr0
onboot: 1
ostype: w2k8
sockets: 1
root@vmserver:~# qm config 102
boot: cdn
bootdisk: virtio0
cores: 4
cpuunits: 200000
ide0: local:102/vm-102-disk-1.qcow2,format=qcow2,size=76G
ide1: local:102/vm-102-disk-3.qcow2,format=qcow2,cache=writeback,size=76G
ide2: local:iso/virtio-win-0.1-52.iso,media=cdrom,size=57126K
memory: 3072
name: SBS2003
net1: virtio=CA:01:F5:81:EF:87,bridge=vmbr0
onboot: 1
ostype: wxp
sockets: 1
unused0: local:102/vm-102-disk-2.raw

What kind of additional infos would you need?