Comment 30 for bug 889423

Hmm, ok, I'm a bit surprised that bond0 still doesn't get added to the bridge.

What's supposed to happen with that new ifenslave at boot time is:
1) One of the network card gets detected and sends a udev event
2) Upstart picks up the event and brings up the interface
3) As the interface is part of a bond, bond0 is brought up first
4) Usually around that time, the second interface is detected and also triggers upstart
5) This card is put on hold waiting for the bond to be ready
6) bond0 is done initialising
7) The first network card is added as a slave
8) bond0 is now up and ready with one slave and can be bridged from this point on
9) The second network card is added as a slave
10) All of eth0, eth1 and bond0 are now up and working
11) At some point later in the boot sequence, "ifup -a" is called by the networking.conf upstart job, creating br0.

So it's not completely impossible that 11) actually happens before 8) but that'd most likely be cause by something taking a lot longer than it should when initialising the bond or the interfaces.

Did you happen to see brctl's error message?
It could be two things:
1) Complaining that bond0 doesn't exist
2) Saying Operation not permitted, meaning that bond0 exists but has no slaves and so no mac address at this point