I am not experiencing this issue. However I did get whacked when upgrading my iPhone which then decided to use GMails unread count to determine what I had not read. That was very frustrating, I went from a dozen or so unread on my phone to thousands. The easy solution was to flag it all read at Gmail and my phone calmed down.

I am going to assume that is why I am not being hit with this issue he mentions. Both my mail accounts on my iMac are just fine. Still never understood Apple's fascination with requiring three keys just to mark a message as read.