When I have put a message in the trash, I do not want to see it, and yet when I get another email from the same recipient, somehow, the message in trash is included and at the top there is a banner saying that the thread includes messages in trash.
Who thought this was a good idea? Just saying, I throw messages out for a reason, and that reason is not to see them again. At a minimum, adding a setting to omit deleted messages from a thread should be available.