tedster - 6:54 pm on Apr 17, 2010 (gmt 0) [edited by: tedster at 8:10 pm (utc) on Apr 17, 2010]
I have seen this kind of thing now and then over recent years - at least I've seen websites with no "obvious" inbound links that still have PR-3 or PR-4 for some of their pages. Usually there are scraper sites and what have you that are linking, but such backlinks don't appear on Google's link: operator or WMT.
Why does this happen? I have a suspicion that it is related to what Matt Cutts once said - that Google has a few things they do to help "Mom & Pop" sites compete with the heavy hitter websites.
[edited by: tedster at 8:10 pm (utc) on Apr 17, 2010]