does not bind to existing virtual bridge

Create bridge with brctl (host only) assign an IP-Address to this bridge, configure NAT on this bridge.
Check the bridge running with KVM or QEMU.
Install virtualbox
Install some flavor of linux on a created VM inside VirtualBox
Bind the network interface to your own bridge

Awaited:
Works. dhcp getting config information as KVM/QEmu-Guests do.

Real results:
No IP-Address, no notwork connection. Just not working.

ProblemType: Bug
DistroRelease: Ubuntu 11.04
Package: virtualbox 4.0.8-dfsg-2ubuntu1~natty1
Uname: Linux 2.6.39.2 x86_64
Architecture: amd64
Date: Thu Jul 7 18:00:27 2011
ProcEnviron:
 LANGUAGE=de_DE:en
 LANG=de_DE.UTF-8
 SHELL=/bin/bash
SourcePackage: virtualbox
UpgradeStatus: Upgraded to natty on 2011-05-21 (47 days ago)