When you select "Reply" it's not automatically selected to reply to the person that sent the last e-mail, instead it's defaulted to the person/contact who is connected to the ticket.
With this in mind it would be good to update so when selecting "Reply" OR "Reply all" the feature should work as following:
Reply:
Default "To": The person who the e-mail you selected "reply" on.
Default "CC": Empty
Reply all:
Default "To": The person who sent the last e-mail.
Default "CC": All people that where in "CC", as well as all others who where in "To", in thee-mail you selected "reply all" on.
