tedster - 3:59 am on Aug 6, 2011 (gmt 0)
This kind of site: oddity can mysteriously appear from time to time and then just as mysteriously disappear. It is worth watching, but if your traffic and rankings don't change at the same time that the site: operator results go buggy, it may just be that mysterious "something" that happens. Google's back end data can get very weird when it comes to reporting functions as opposed to real keyword search results.
That said, sometimes I've seen it show up at the same time as what appears to be an algorithmic spam demotion. In that case, it's the algorithmic hit that matters most, and the site: operator results are a secondary sign.
I wish I could say it's cut and dried... but I've seen a lot of strangeness in this area and can't pretend to have it 100% figured out.