When you certify a key with user ID "Jane Doe <jane@example.net>" then the Certify dialog has the title "Certify Certificate: Jane Doe - Kleopatra". When you do the same with a key with email-only user ID "jane@example.net" then the title is "Certify Certificate: - Kleopatra".

I think in the email-only case the title should be "Certify Certificate: jane@example.net - Kleopatra".