Sorry, Till, for wasting your time
I found the answer today:
Submitted by Damian (not registered) on Wed, 2009-03-25 17:01.
Very important to know...
To make PureFTPD show hidden files you have to create a new file "DisplayDotFiles" in "/etc/pure-ftpd/conf/" with the value "yes". Falko or s.o. else already mentioned it in the english ispc forum, but i think this setting belongs to a "PERFECT" server
echo "yes" > /etc/pure-ftpd/conf/DisplayDotFiles
My OS is Ubuntu. Thanks!