Until recently, -net options used to add interfaces to linux in the same order they went on the command line, so the first one you listed on the qemu command line would become eth0, the second -net became eth1, and so on. Now they're added in _reverse_ order, so the _last_ one on the command line is eth0.
I bisected the behavior change to commit 60c07d933c66c4b30a83b7ccbc8a0cb3df1b2d0e but don't understand why it changes this behavior. (Probably making udev do something stupid, but it happens consistently both before and after...) Rob
