avahi-ui is trampling files that should be "owned" by avahi's in do_populate_sysroot. It needs to stop doing this as it causes a race and has broken things on the autobuilder (e.g. pulseaudio failed as avahi went missing).
Fixed in master in http://git.yoctoproject.org/cgit.cgi/poky/commit/?id=29a04dc676b26bf3f242c42a9be1630acc6fff22