Oh, and in the share/doc directory of the union: lrwxrwxrwx 1 root root 71 Dec 31 1969 expat -> /gnu/store/2q8wwhd3prib0swky68rbx9hl0xxs6hf-expat-2.4.3/share/doc/expat/ lrwxrwxrwx 1 root root 77 Dec 31 1969 expat-2.4.1 -> /gnu/store/2q8wwhd3prib0swky68rbx9hl0xxs6hf-expat-2.4.3/share/doc/expat-2.4.1 Second link broken, first link correct, both to the replacement (2.4.3 version) store directory.