I noticed these warnings on uninstallation (printed out multiple times):
# apt-get purge -y webmin
(snip)
Running uninstall scripts ..
Use of uninitialized value in string eq at /usr/share/webmin/time/time-lib.pl line 23.
(snip)
Use of uninitialized value in string eq at /usr/share/webmin/servers/servers-lib.pl line 396.
Thanks for reporting this - it's harmless, but we'll fix it in the next Webmin release.