With rRPK7c07ad1d427cd9c75fc4c40fe15c520b5b046273 (as in current Winterfell) in plugins/calendar/drivers/kolab/kolab_driver.php for $cal instanceof kolab_storage_folder_user the following line was added:

'title'    => $cal->get_owner(),

But shouldn't that be instead:

'title'    => $cal->get_title(),

This would be at least consistent with all other calendar types in the same file (given they're using get_title() already).