If you build in pbuilder, no systemd is installed and so the flag is set to false which means the files will not get installed. Adding the explicit flag will make sure they are included in the package.
These are included in the right version via the suggested installation of build-essential, which which installs the right lib via dependencies: g++ -> g++-<version> -> libstdc++-<version>
Adding it explicitly meant always adding new versions :-(
This reverts commit b47dd70f35.
This could trigger a infinite loop between the timer unit (running a sync and changing the griveignore file at the start) and the changes unit (reacting to the griveignore change and retriggering the sync).