Courier not listening on IPv4 ports

I am having an issue with postfix/courier after a software update in which courier is no longer listening on the IPv4 ports. Here is the netstat output:

ubuntu@ip-10-x-x-x:~$ sudo netstat -plnt
sudo: unable to resolve host ip-10-0-4-32
Active Internet connections (only servers)
Proto Recv-Q Send-Q Local Address           Foreign Address         State       PID/Program name
tcp        0      0 127.0.0.1:783           0.0.0.0:*               LISTEN      1178/perl       
tcp        0      0 0.0.0.0:465             0.0.0.0:*               LISTEN      3841/master     
tcp        0      0 0.0.0.0:22              0.0.0.0:*               LISTEN      1078/sshd       
tcp        0      0 0.0.0.0:25              0.0.0.0:*               LISTEN      3841/master     
tcp        0      0 127.0.0.1:10024         0.0.0.0:*               LISTEN      1173/amavisd-new (m
tcp        0      0 127.0.0.1:10025         0.0.0.0:*               LISTEN      3841/master     
tcp        0      0 127.0.0.1:3306          0.0.0.0:*               LISTEN      1127/mysqld     
tcp        0      0 0.0.0.0:587             0.0.0.0:*               LISTEN      3841/master     
tcp6       0      0 :::110                  :::*                    LISTEN      1854/couriertcpd
tcp6       0      0 :::143                  :::*                    LISTEN      4172/couriertcpd
tcp6       0      0 ::1:783                 :::*                    LISTEN      1178/perl       
tcp6       0      0 :::22                   :::*                    LISTEN      1078/sshd       
tcp6       0      0 :::993                  :::*                    LISTEN      4124/couriertcpd
tcp6       0      0 :::995                  :::*                    LISTEN      1883/couriertcpd

As you can see, ports 110, 143, 993, and 995 only appear to be open on the IPv6 interface. This is causing connectivity problems for several mail clients.

Here are my config files:

In /etc/postfix/main.cf, I have

inet_interfaces = all
inet_protocols = ipv4

In /etc/courier/imapd-ssl.dist, I have:

SSLPORT=0.0.0.0.993
SSLADDRESS=0.0.0.0

In /etc/courier/imapd.dist, I have:

PORT=0.0.0.0.143
ADDRESS=0.0.0.0

And of course I did:

sudo /etc/init.d/courier-imap restart
sudo /etc/init.d/courier-imap-ssl restart

And no luck...

As a temporary fix, I have added a public DNS entry for the IPv6 address of this host, and mail seems to be coming in now.

PORT/SSLPORT should not be anything but the port number 110 or 143 or 993 or 995