martinibuster - 9:58 pm on Jul 19, 2011 (gmt 0)
There was no miscalculation or rollback. The latest toolbar PR is simply more recent than what was previously shown. Vanessa Fox wrote an excellent article [searchengineland.com] explaining how Twitter bungled their code infrastructure, causing the toolbar to reflect a PR of Zero. Twitter fixed the issue and Google did a refresh of the toolbar data to reflect this.
A Google spokesperson told us:
“Recently Twitter has been making various changes to its robots.txt file and HTTP status codes. These changes temporarily resulted in unusual url canonicalization for Twitter by our algorithms. The canonical urls have started to settle down, and we’ve pushed a refresh of the toolbar PageRank data that reflects that.
Those interested in how redirects and coding can affect what the toolbar is showing should definitely read Vanessa's article at SearchEngineLand [searchengineland.com], it's a good read.