I have continued to carefully test this "bug" as originally observed. I could originally replicate the initial problem statement (reply from wrong email address) when replying to messages that had been Moved to a new folder -- that has now been fixed.
However, a side issue now clearer since that correction, is that a Reply All to a message that has been so Moved will included your own email address. However, that cannot be replicated with 1) any message that has remained in the original Inbox, nor 2) with any messages opened via their inclusion in a Smart Mailbox, but not Moved.
To summarize, I can only replicate the issue with inclusion of your own email address in the distribution on messages residing in a mailbox folder to which they have been Moved from the receiving Inbox. A message Copied to such a folder, but also left in the original Inbox will demostrate the issue when replying to the message from the folder, but will not when replying from the message still residing in the Inbox.
On those few catagories of messages I Move to a specific folder, it has not been a problem, and I don't worry about it. Most of my email processing takes place in the original Inbox, and there it is not a problem. If a Smart Mailbox is used to provide a segration of certain types of emails that remain in the receiving Inbox, it will not be a problem there, either.
Ernie