"error sending to idled"

[Adam Tauno Williams]

Cyrus IMAPd 2.2.8

In /etc/cyrus.conf I have:
SERVICES {
...
  idle          cmd="idled" listen="/var/lib/imap/socket/idle" prefork=0
...
}

And in /etc/imapd.conf I have:
idlesocket: /var/lib/imap/socket/idle

And the idle socket exists and is being listened to:
sardine:/etc # fuser -u /var/lib/imap/socket/idle
/var/lib/imap/socket/idle: 15835(root)
sardine:/etc # ps ax | grep 15835
15835 ?        Ss     0:06 /usr/lib/cyrus/bin/master
-p /var/run/cyrus.pid -d
18833 pts/1    S+     0:00 grep 15835

But I continuously see messages in the log file like:
imap[18492]: error sending to idled: 2

And I don't see any idled processes running:
sardine:/etc # ps ax | grep idled
18841 pts/1    S+     0:00 grep idled
sardine:/etc #

What am I missing?