You're not stupid at all! This is definitely a bug.
When the package is built, WPrefs is installed in /usr/share/lib/GNUstep and the menu points there. But then for some reason, the Debian/Ubuntu package *moves* WPrefs to /usr/lib/GNUstep.
I'll upload a new version soon that fixes this and *doesn't* move WPrefs. It will be uploaded to Debian and should migrate over to Ubuntu in time for bionic.
You're not stupid at all! This is definitely a bug.
When the package is built, WPrefs is installed in /usr/share/ lib/GNUstep and the menu points there. But then for some reason, the Debian/Ubuntu package *moves* WPrefs to /usr/lib/GNUstep.
I'll upload a new version soon that fixes this and *doesn't* move WPrefs. It will be uploaded to Debian and should migrate over to Ubuntu in time for bionic.