I could reproduce this weird behaviour. First I thought that there might be some pages linking to the error page with the anchor text in question - this is also what the cache page claims. Also there are many scraper and auto generated spam sites with broken links that never really show up in the Google index.
Similar cases have happened before. There is a forum by Google for Webmasters where you can tell Google about problems with your website:
Similar cases have happened before. There is a forum by Google for Webmasters where you can tell Google about problems with your website:
http://www.google.com/support/forum/p/Webmasters?hl=en
You could tell them your findings and maybe someone from the Google team will look into the matter, if you are lucky.