peculiar zsh completion issue

[Fourhundred Thecat <400thecat@gmx.ch>]

Hello,

I am experiencing a very peculiar issue with zsh completion:

On a server where dovecot is installed, suddenly zsh completion does not
work for any keyword containing the keyword "dovecot".

For instance:

  cd /etc/do<TAB>
  service do<TAB>
  chkconfig do<TAB>
  nano /etc/default/do<TAB>

Also, when I do just service <TAB>, then all possibilities are listed,
(ie, all executable files in /etc/init.d/) but dovecot is  not listed as
possible completion. As if it did not exist.

All of the above examples work for any other package / file / path.

If I try the same on a machine where package dovecot is not installed,
and just create dummy files in the paths:

  /etc/dovecot/
  /etc/init.d/dovecot
  /etc/default/dovecot

then completion works normally.

I am using zsh 5.7.1 on Debian Buster.

thanks,