A known bug in ssh-copy-id btw: [ssh-copy-id] Do not treat Dropbear special by MichaIng · Pull Request #250 · openssh/openssh-portable · GitHub
This is the commit which broke it (“as in OpenWRT” means special handling for non-default Dropbear usage…): git.hands.com Git - ssh-copy-id.git/commit
Sadly Philip is not answering my emails.