As discovered in bpo-41509, relpath can strip spaces, so match that expectation.

Author: jaraco

setup.py

@@ -117,7 +117,7 @@ def _restore_install_lib(self):
         """
         suffix = os.path.relpath(self.install_lib, self.install_libbase)
 
-        if suffix == self._pth_contents:
+        if suffix.strip() == self._pth_contents.strip():
             self.install_lib = self.install_libbase