I just noticed and found that one of the internal pages of my site got PR 4 recently! The page is for Search Engine Friendly Directories which gives a list of many directories, free and paid, where you can submit your website. The page jumped from PR 0 to PR 4 due to the links coming back to it. Some data centres still show PR 0, whereas the others show Page Rank 4.
You can see the PR changes on different data centres using this PR check tool.