As you might have noticed from the comments on the blogpost on the new version of Courier-auth, there was something wrong.
It turned out to be a completely different error than first reported. Everything looked allright after compiling and installing but it all went wrong when trying to start it up:
/usr/local/var/spool/authdaemon/pid.lock: Bad file descriptor
ll_daemon_start: Resource temporarily unavailable
I checked permissions, deleted the files, to no avail. At a loss I posted a question to the courier-user mailinglist and I got a reply and a patch within a few hours. I’ve just tested the patch and it all works as expected.
Now we only need to wait for the official release of the patch into the next release.