I had a right sidebar that I added some product images and text (partly copied from Amazon) on the right sidebar of each page. It NEVER occurred to me that this was the problem, until I read of your changes. I was so focused on finding duplicate content (not much, if any, worth worrying about)… but it never occurred to me that that content IN THE SIDEBAR was the issue. I had eight or nine products with excerpted text … about 10~12 words for each edited from Amazon’s content, and wow!
And the weird thing: Copyscape was NO help diagnozing this problem. In fact, I’m really not sure that copyscape’s real value is, and I pay for searches, too! Copyscape just didn’t spot these issues, despite the fact it was on EVERY page of mine, and dozens of other shopping sites… too.
I don’t know if that will fix the problem or not. Perhaps Google turned up the duplicate content filter to max now! Anyway, I have to find some way to fix my problem.