samba - Mar 2012 - Many usershare messages logged but no usershares defined

There are many messages about samba usershares in the logs but no
usershares are defined:

# grep '\[2012/03/20' /var/log/samba/log.smbd | grep
process_usershare_file | wc -l
1518
# grep --ignore-case usershare /etc/samba/smb.conf.source /etc/samba
/smb.conf
[no output]
# ls -l /var/lib/samba/usershares/
total 0

The messages are typically like:

[2012/03/20 10:05:05.002947,  0]
param/loadparm.c:8686(process_usershare_file)
  process_usershare_file: stat of /var/lib/samba/usershares/<share name>
failed. No such file or directory
[2012/03/20 10:05:05.004924,  0]
param/loadparm.c:8686(process_usershare_file)
  process_usershare_file: stat of /var/lib/samba/usershares/<share name>
failed. Permission denied

One example shows ~100 lines like that in one second, probably caused by
a user running an application that has its data on that share.

Often these messages are accompanied by one or two messages like these

Mar 20 10:05:01 LS1 smbd[31614]: [2012/03/20 10:05:01.166801,  0]
../libcli/auth/ntlm_check.c:54(smb_pwd_check_ntlmv1)
Mar 20 10:05:01 LS1 smbd[31614]:   smb_pwd_check_ntlmv1: incorrect
password length (64)


The <share name>s seen are the only two public writeable shares on the
server.

Here is smb.conf (global and affected shares)
===== smb.conf begins ====[global]
	workgroup = ACUR
	server string = Server
	security = SHARE
	smb ports = 139
	load printers = No
	preferred master = Yes
	domain master = Yes
	wins support = Yes
	remote announce = 10.8.0.6/ACUR 10.8.0.10/ACUR 10.8.0.14/ACUR
10.8.0.18/ACUR   10.8.0.22/ACUR 10.8.0.26/ACUR 10.8.0.30/ACUR
10.8.0.34/ACUR 10.8.0.38/ACUR   10.8.0.42/ACUR 10.8.0.46/ACUR
10.8.0.50/ACUR 10.8.0.54/ACUR 10.8.0.60/ACUR   10.8.0.64/ACUR 10.8.0.68/ACUR
	guest only = Yes

[Intranet_Mapping]
	comment = Intranet Mapping (MapInfo)
	path = /srv/samba/Intranet_Mapping
	read only = No
	guest ok = Yes

[LadA share]
	comment = Replacement for the Viji share
	path = /srv/samba/LadA
	read only = No
	guest ok = Yes
===== smb.conf ends ====
The server is Debian Squeeze running samba 2:3.5.6~dfsg-3squeeze6. The
clients are a mixture of Windows 7 and XP.