Just received the following e-mail from support:
> Further to your last contact with the Helpdesk regarding the issue
> with the WZR2-G300N access point, as discussed I raised this
> issue with the Product specialist to be investigated. He has
> confirm that the issue is down to a bug in the firmware in relation
> to MAC address's that do not start with 00 (similar to the issue for
> US routers) and it has been escalated on to our development team
> in Japan to be fixed.
>
> As soon as I have any further updates I shall be in touch.
Again, good work Rivashin for spotting the relation to the client's MAC address. Maybe we don't need to upgrade our routers after all :-)