How to reproduce: create virtual machine with <interface type='bridge'> <source bridge='br0'/> <target dev='acp30_ext'/> </interface> and try to virt-clone it. MAC-address will be changed. but "acp30_ext" will not be changed, so virtual machine will not run simultaneously with original virtual machine.
Thanks, upstream now: http://git.fedorahosted.org/git?p=python-virtinst.git;a=commit;h=bf9a72ee694e0b688b255b4236343b05aeb2a706