"IPv6 duplicate address" in Linux

My Linux system (Ubuntu 12.10) was suddenly having problems with IPv6, and dmesg said:

IPv6: wlan0: IPv6 duplicate address 2a00:cd8:blabla:1af4:6aff:fe9c:ced4 detected!
IPv6: ipv6_create_tempaddr: regeneration time exceeded - disabled temporary address support

The workaround was to disable Duplicate Address Detection (DAD) for the IPv6 privacy extensions on my Wifi interface wlan0:

sudo sysctl net.ipv6.conf.wlan0.accept_dad=0

Please note: if you use wired ethernet eth0, you should do something like this:

sudo sysctl net.ipv6.conf.eth0.accept_dad=0

It is unclear to me where the problem is: in Linux itself , or in my modem, or in the interaction between Linux and my modem.
The problem also occurs in OpenSuSE 12.2 on the same LAN, so it's not a Ubuntu-only problem.

Bug report is here: https://bugs.launchpad.net/ubuntu/+source/linux/+bug/1120617

Update: it seems to be related to Wifi; it does not happen with wired ethernet.