suse and passwd shadow problem

os: suse v6.4 platform: ibm 300pl other app: webmin v0.82 other app: squid v2.3s3 to all you webmin admin out there... problem: user account added via webmin; some time after that, account fanishes from /etc/passwd and/or /etc/shadow. go back into webmin and add exact same account again. but it fails when challenged by squid. so back into webmin and add a character to end of account name, save, and challenge gets authenticated!! normally, adding an account in passwd/shadow, by unix rules, is fairly straightforward and problem free. any ideas why this is happening and how to solve/troubleshoot it?? rf