Thanks for the hint. I suspect that LE ignored my selection of just one domain from the list of domains in the “Which names would you like…” list. Although “horde.webmail” isn’t even in that list.
Starting with -d shopping-list.eu from the command line made this error go away. Looks to me as if selecting a domain from the list shows a different behavior from entering it on the command line. Bug or feature?
That does sound like a potential bug in the client. Can you file an issue at https://github.com/letsencrypt/letsencrypt, and include the logfile you attached, or link to it? The client team may also want to see a copy of your Apache configs if you are willing to provide.