unbound 1.9.6 fails to load as a systemd service on Ubuntu 18.04.3 LTS, when built from source and using the included contrib/unbound.service file.

unbound was built and installed using the following command line:

./configure --enable-systemd --with-libevent && make && make install && ldconfig

The following error message appears in journalctl:

unbound.service: Failed to set up mount namespacing: No such file or directory
unbound.service: Failed at step NAMESPACE spawning /usr/local/sbin/unbound: No such file or directory
unbound.service: Main process exited, code=exited, status=226/NAMESPACE
unbound.service: Failed with result 'exit-code'.

I narrowed it down to this line in unbound.service:

BindPaths=-/usr/local/etc/unbound/unbound.pid:/usr/local/etc/unbound/usr/local/etc/unbound/unbound.pid

I'm not sure why this causes /usr/local/sbin/unbound to not be found, but when I comment out the line, unbound works as expected. The line itself looks pretty strange, with the duplication of /usr/local/etc/unbound.