Duply adds an AT (@) before the path (Ubuntu 16)

After an update from Ubuntu 14 to Ubuntu 16, duply stopped working - or rather continued working, but stored the backup files into the wrong directory.

This is the duply configuration (excerpt):

TARGET='file:///mnt/backup/server'
TARGET_USER=''
TARGET_PASS=''

And here's what ps -aux tells me when the backup is started:

python2 /usr/bin/duplicity --name duply_server --encrypt-key XXXXXXXX --sign-key XXXXXXXX --verbosity 4 --full-if-older-than 14D --force --exclude-filelist /root/.duply/server/exclude / file://@/mnt/backup/server

Note that AT sign (@) in the filename (last parameter). When run from /root/, It causes duplicity to create a folder /root/@/mnt/backup/server to store the backup there. I am unsure if this is a change in the behavior of duply, duplicity or python. Any idea how to solve this and tell duply the full folder, as it used to work?

Edit

For now, I assume, it's a bug in duply which tries to add a user name to the folder, as required for ftp.

My workaround is to create a symbolic link /root/@/mnt -> /mnt, but that's nothing more than a workaround. So thank you very much for better ideas!