I think I know what happened.
When you enter an '@yahoo.com' email address, the email app automatically uses a new set of servers. I'm doing IMAP right now, and the IMAP and SMTP yahoo servers have 'android' in the name.
I think the only change they made to the email app was for it to default to those servers if you used Yahoo. I bet Yahoo on their end set up new servers so that we wouldn't have the million Sent Items issue.
But, no, unfortunately. Someone on this thread has already said they still ARE getting extra copies of sent messages in their sent folder,,,only about 25 extra copies per email, but still...say it ain't so....:icon_evil: