Address list group syntax, as described in RFC 5322 (https://tools.ietf.org/html/rfc5322#section-3.4) is of the form "group1: adress1@example.org, <address2@example.com>;". It is most often used to indicate undisclosed recipients, i.e., as "undisclosed-recipients:;". Current support in kmail is not so good: entering such a group seems not to be possible and group names are not shown when receiving such a message.
Thank you for reporting this issue in KDE software. As it has been a while since this issue was reported, can we please ask you to see if you can reproduce the issue with a recent software version? If you can reproduce the issue, please change the status to "REPORTED" when replying. Thank you!
Still problematic.