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It's very weird because this site still ranks #1 for most of it's keywords and many internal pages and has not been hit with the SERP issues like my other sites.
Also, another site I have which is newer went from PR1 to PR0 as well.
Could there be another update underway or is this some kind of glitch, checked with several tools and they all show same?
If this is a penalty on me personally, would they wait for an actual update or just lower the PR at any time?
Have you been able to diagnose any reason for the -50?
Three of my sites are also there.
On my end the only thing they have in common is a low amount of links and links of fairly low value.
I can confirm that there has been again changes in toolbar PR in couple of sites I am watching. All changes I am seeing affect internal pages and yet again all PR changes were between some PR --> no PR and no PR --> some PR