Earlier quoted context omitted.
When logged in on the balance page it says: "DO NOT DEPOSIT TO PREVIOUSLY PROVIDED BITCOIN DEPOSIT ADDRESSES. Deposits sent to previous address will not be honored. New deposit addresses are forthcoming.".
Well, at least they're doing that. But there's still no explanation on their site, blog, Twitter, or Facebook, and it's after 8 AM on Monday in London. Expect this to start hitting the financial press in London in the next hour or two.
edit: whoops, added to the FT Alphaville article! http://ftalphaville.ft.com/2015/01/05/2079012/who-needs-cave... Come in via Google News for full text. They're using it as one example in a piece on how Bitcoin's infrastructures and the community's ability to assess expertise are not very good.