I also encountered this. My working hypothesis is that it may be related to this (from README.Debian):
> Since version 1.6-6 we support multiple stanzas of the interface usefull, > for example, to describe the IPv4 and IPv6 addresses of an interface. The > only requirement for this is that all of them need to have bridge_ports > specified. Could you try duplicating the bridge_ports in the inet6 stanza and see if that eliminates the problem? Alternatively, perhaps adding dad-attempts 0 would work. I have not yet been able to try either remedy. Please let me know if one of them helps. -- Rob Leslie r...@mars.org