Problem proxmox change vmbr to VM in hotplug

HI, I have installed the proxmox 2.3. I have installed ubuntu in VM kvm with network virtual vmbr0 to net0 for VM. Ii's works very well. But I like change the vmbr0 to vmbr4 in hotplug...

I saw this link http://pve.proxmox.com/wiki/Manual:_vm.conf

Exactly:

hotplug: boolean
Allow hotplug for disk and network device Default value is '0'.

I'm interesting in network.

But I get this error with change vmbr0 to vmbr4 in hotplug:

VM 403 qmp command 'netdev_del' failed - Device 'net0' not found (500)

Could do otherwise? Can I help me please? Is possible?

I like very much proxmox, I've been using a long time

Sorry for my english.

Thanks in advanced.