Files:
/etc/default/pure-ftpd-common
/etc/inetd.conf

- - -

pure-ftpd startoption "standalone" (nessecary for virtualusers with
VIRTUALCHROOT)
gets blockes by inetd (this is the default startoption)

# Configuration for pure-ftpd
# (this file is sourced by /bin/sh, edit accordingly)

# STANDALONE_OR_INETD
# valid values are "standalone" and "inetd".
# Any change here overrides the setting in debconf.
STANDALONE_OR_INETD=standalone

# VIRTUALCHROOT:
# whether to use binary with virtualchroot support
# valid values are "true" or "false"
# Any change here overrides the setting in debconf.
VIRTUALCHROOT=true

- - -

Fix: manually comment out
ftp    stream  tcp     nowait  root    /usr/sbin/tcpd
/usr/sbin/pure-ftpd-wrapper
(it binds ftp port 21 and prevents pure-ftpd to startup in standalone mode)

#:STANDARD: These are standard services.
telnet          stream  tcp     nowait  telnetd-ssl     /usr/sbin/tcpd
#/usr/sbin/in.telnetd
#ftp    stream  tcp     nowait  root    /usr/sbin/tcpd
#/usr/sbin/pure-ftpd-wrapper

#:BSD: Shell, login, exec and talk are BSD protocols.

#:MAIL: Mail, news and uucp services.

#:INFO: Info services

- - -

It would be nice, if the wrapper script could handle this issue, since ist
is controlled by the
default script option.

P.S.
took me hours to find out, why VIRTUALCHROOT did not work !
(was cused by this starup issue) :-/