Path name operations in IronPython.Runtime.Importer are supposed to be performed through the PlatformAdaptationLayer, enabling platform adaptations of path name structure. Some operations are still directly done to System.IO.Path, though, which breaks the adaptation layer. The commit https://github.com/rickardraysearch/main/commit/7cc9ed676c1ee6f6f0e770d9c8842d24b4e1c7d6 fixes (at least some of some of) the remaining items.