shit takes time when google is suspicious of incoming links
they will pass pagerank along after a time frame for a link like this, it isn't just hit your shit hard with paid links and skyrocket to the top
they built into their algorithm resistance homey so that paid links dont appear affective and so that people cant just buy their way to the top of google.
Ground reality is something different from the levels you are watching it!
Large companies on the net are buying (and selling) links... I know because I have worked closely with at least one such market leader of UK. Google would never know how those transactions are done, and of course they wouldn't hurt the large online companies simply because they traded links... Your debate would hold true though in cases of natural and unnatural links, and that too when the sites grow their backlinks abnormally (but this is only a personal opinion because no one actually knows how G functions).... When you observe the cases and are a keen watcher of actual happenings (links trading and getting away with it) then you know certain truths...
If you know (you won't anyway) the reality behind why OP's link isn't working despite the fact that the site has a true PR8 (because, atm, it's very hard to prove otherwise and all sites that can prove it false are atm saying that the PR8 is real). Read the posts carefully and you might make something out of it...
Anyone in OP's place would have purchased that genuine PR8 backlink considering at all 'positive' things there, but he possibly missed out one bitter fact: about the overall background and why that campaign was going to definitely fail... imho.
The circumstances that made the owner of that site a (sad) loser was mentioned by that owner in another context while he wanted to sell one of his numerous sites some years ago. His own high-PR still stays intact and may be has grown since then, but no one is coming forward to do any links-purchasing business with him because of unavoidable restrictions faced by his sites - again imo.
As Gyuman told OP very rightly that the site is flagged (he added "may be" to it, but looking into it minutely it looks true that the site is definitely flagged because of more complex reasons than what I have mentioned in this post).