Right, that's the expected result. RoundCube can never know initially who you are, where you live, what info you want added to your identity. So you have to manually add it.
There's no way around this. Prior to emailing, you should populate your identity in your preferences, that way certain info is filled out for you. I don't know what else to tell you. RoundCube doesn't know any information about the user logging in, so you have to supply it. That's just part of the program. It's just like Thunderbird or Outlook. Neither of them know your name, or what your reply-to address and signature will be. So they let you fill it in. Same thing in RoundCube. Each user will have to edit their own identities.