Trying to find a simple way to reproduce
and I could verify the problem.

Testing with rev:095db27e80644a2a547f6e66a58207981352323d 2019-03-13

== Reproduction with demo.py failed
python3  ./demo.py -t jinja2 -b sqlite nuke
# and python2

worked and had 
# Database backend.
# Default:
backend = sqlite
in ./demo/config.ini

== Reproduction with install
mkdir test-install/
cd roundup-hq
python3 setup.py install --prefix=../test-install
# setting PATH and PYTHONPATH with fishshell
set -l base /home/bern/roundup/test-install
set PATH $base/bin $PATH
set PYTHONPATH $base/test-install/lib/python3.5/site-packages/:$PYTHONPATH

mkdir test-tracker
roundup-admin -i test-tracker install jinja2 sqlite
roundup-admin -i test-tracker initialise 1234