It is not possible to remove events from caldav calendars. The event is removed from the korganizer view, but not from the server. Moreover, after trying to delete an event the resource becomes broken and it's not possible to syncronize the calendar anymore. Under akonadiconsole, the caldav resource shows the message: "There was a problem with the request. The item has not been deleted from the server. The file or folder [[server URL]] does not exist."
*** This bug has been marked as a duplicate of bug 355441 ***