/var/log/auth spam every 2 mins: sshd[*]: Connection closed by 127.0.0.1 [preauth]

Description: Ubuntu precise (development branch)
Release: 12.04

openssh-server-1:5.9p1-4ubuntu1

Not really sure that OpenSSH is the real culprit, but it's what has been reporting the log spam since I upgraded from 10.10 to 12.04 a day or two ago:

$ sudo grep 'Connection closed by 127.0.0.1' /var/log/auth.log | tail
Mar 26 14:27:19 perry2 sshd[16380]: Connection closed by 127.0.0.1 [preauth]
Mar 26 14:29:19 perry2 sshd[16383]: Connection closed by 127.0.0.1 [preauth]
Mar 26 14:31:19 perry2 sshd[26767]: Connection closed by 127.0.0.1 [preauth]
Mar 26 14:33:19 perry2 sshd[7300]: Connection closed by 127.0.0.1 [preauth]
Mar 26 14:35:19 perry2 sshd[19270]: Connection closed by 127.0.0.1 [preauth]
Mar 26 14:37:19 perry2 sshd[31926]: Connection closed by 127.0.0.1 [preauth]
Mar 26 14:39:19 perry2 sshd[1696]: Connection closed by 127.0.0.1 [preauth]
Mar 26 14:41:19 perry2 sshd[1700]: Connection closed by 127.0.0.1 [preauth]
Mar 26 14:43:19 perry2 sshd[1703]: Connection closed by 127.0.0.1 [preauth]
Mar 26 14:45:19 perry2 sshd[1709]: Connection closed by 127.0.0.1 [preauth]

$ sudo zgrep -c 'Connection closed by 127.0.0.1' /var/log/auth.log*
/var/log/auth.log:934
/var/log/auth.log.1:595
/var/log/auth.log.2.gz:0
/var/log/auth.log.3.gz:0
/var/log/auth.log.4.gz:0

$ ll /var/log/auth.log*
-rw-r----- 1 syslog adm 128K Mar 26 14:52 /var/log/auth.log
-rw-r----- 1 syslog adm 132K Mar 25 07:52 /var/log/auth.log.1
-rw-r----- 1 syslog adm 2.1K Mar 23 16:25 /var/log/auth.log.2.gz
-rw-r----- 1 syslog adm 18K Feb 26 07:45 /var/log/auth.log.3.gz
-rw-r----- 1 syslog adm 19K Feb 19 07:45 /var/log/auth.log.4.gz