Kolab Winterfell has ended up in a state that is dysfunctional — I warned you it would, and now it has. I love being right.
(… silence for applause …)
It is the Guam packages that has received a fix for T1028: It did not parse all LIST, XLIST and LSUB commands correctly. As a side-effect though, the tests that create the mailboxes (using the Kolab daemon) never gets its listing of mailboxes to complete the expected number of folders (since folders containing groupware are suppressed).