A AdSense Help thread has confirmed reports from Google that some (not many) publishers may have had a hold on their account for about four months due to a bug. That means, these publishers were not paid for around four months due to an issue with a specific feature of the site.

As explained by Ashley from Google:

It is nice that Google will be paying out what is due to this publisher, but a four month delay and nothing extra for that?

Forum discussion at AdSense Help.