Why would position drastically change with same PR?

Unaltered site, same keywords, same PR, but a new position.

[grahamstewart]

Have the recent updates majorly altered the order in which Google returns its findings?

For instance, I have a site with a PageRank of 5 that used to appear in the 7th position for it's keywords. Now it appears 41st for the same keywords.

The site has not been altered in any way and the GoogleBar still reports its PR to be 5.

So why are there suddenly so many sites above it (most with much lower PRs and lower actual relevancy to the topic)?