(I consider this a bug report—not sure if this is the place for that)

By clicking on the arrow next to the email in a conversation, I enter a contextual menu that allows me to send a message to that email (or add to contacts, or to VIP etc...) The logical thing to do is to follow the "Global reply" or "Global Send" setting, in my case to use the selected account. However, it always uses my first account.