Forum Moderators: Robert Charlton & goodroi
I have seen similar thing with some SEO company building a network crosslinking all their websites.
these guys spend countless hours asking for reciprocal links and they provide a link back from pages that have PR but NEVER have a Google cache, obviously a scam but I won't how they managed to do that.
It's obviously on purpose in my example (maybe some server config I dunno, but surely nothing as obvious as the no-cache tag or similar) but in yours it could simply be a toolbar error.
You have to know that if the page you are talking about WAS indexed during the latest PR update, it will be given PR until the next update even if the page is an orphan now which could lead Google to not keeping it in cache....my 2 cents but interesting subject.