It is driving me nuts that if I am part of a group of recipients of an email, and I hit "Reply all" then only the one who sent the email I am replying ALL to is put as "To" recipient - the rest are added as CC recipients, even if all were "To" recipients on the email I reply to.
Please either change this - I've never seen another client handle "Reply all" in this way - or at the very least make it a setting on my account (not per client) if I want the current behaviour or the way suggested in this idea.