I have a CalDAV resource for owncloud installed that has been working about fine. I found that it hadn't been synchronizing anymore. I tried to find out why and realized that the password had been changed in the meantime and the CalDAV resource in akonadi had the old one still. It didn't complain in any way and that's what I want to point. There should be an error message when the synchronizing process is not working properly (for example because the password is wrong). Actually I find the interface not very transparent for finding out what went wrong.
It looks like this is a side effect of the error-suppression that was in place. I've just tested with what will become the next release and there's indeed an error message when authentication fails.