I think it would be an improvement to show the source (GPG) in password prompts. When prompt appears and users worked with a program like Claws Mail they probably think that the prompt belongs to Claws Mail which isn't the case. It would be helpful for the understanding of users if the prompt would contain a hint in the title (or the description) where it comes from. Maybe it could also be helpful because they know where a mistake happened and know where to turn right away.