[O] Bug: ORG_ADD_CONTRIB does not work the first time [7.9.2]

[Christopher Schmidt]

I am using the maint as of today (c20730b).

    make "ORG_ADD_CONTRIB=org-contacts" prefix=/tmp/org install

Running this once in a clean org-mode working tree results in org not
copying org-contacts.el(c) to /tmp/org/emacs/site-lisp/org.  Running the
command a second time does that, though.

This is a bug?!

        Christopher