Cyclic dependency? How could this happen?

[toylet]

root at server:/var/run/proftpd # dpkg -r proftpd-common
dpkg: dependency problems prevent removal of proftpd-common:
 proftpd depends on proftpd-common (= 1.2.10-22).
dpkg: error processing proftpd-common (--remove):
 dependency problems - not removing
Errors were encountered while processing:
 proftpd-common
root at server:/var/run/proftpd # dpkg -r proftpd
dpkg: dependency problems prevent removal of proftpd:
 proftpd-common depends on proftpd | proftpd-mysql | proftpd-pgsql |
proftpd-ldap; however:
  Package proftpd is to be removed.
  Package proftpd-mysql is not installed.
  Package proftpd-pgsql is not installed.
  Package proftpd-ldap is not installed.
dpkg: error processing proftpd (--remove):
 dependency problems - not removing
Errors were encountered while processing:
 proftpd

--
  .~.    http://changmw.homeip.net
 / v \  May the Force and Farce be with you! Linux 2.6.16.11
/( _ )\  (Ubuntu 5.10)  10:58:01 up 2 days 18:12
  ^ ^    load average: 1.00 1.00 1.00
news://news.3home.net news://news.hkpcug.org news://news.newsgroup.com.hk
-------------- next part --------------
An HTML attachment was scrubbed...
URL: <https://lists.ubuntu.com/archives/ubuntu-users/attachments/20060428/16099dda/attachment.html>