I installed dokku through the apt repo and trying to run apt-get upgrade to the latest version is running into an error:

...
User 'dokku' already exists
docker:x:999:dokku
gpasswd: user 'syslog
mark' does not exist
dpkg: error processing package dokku (--configure):
 subprocess installed post-installation script returned error exit status 3
Errors were encountered while processing:
 dokku
E: Sub-process /usr/bin/dpkg returned an error code (1)

From what I can tell this comes from the nginx-vhosts/install. In particular the change from f9e636d added the call to gpasswd. As it would happen my server has a group named admin which my user belongs to so egrep ^adm /etc/group | awk -F ":" '{ print $4 }' returns two lines

syslog
mark

and triggers the error. It would seem that changing this regex to ^adm: would match only the adm group rather than all groups which begin with adm but my Debian packaging skills are admittedly sub-par.