I use the ~ character to denote my home directory in
org-publish-project-alist (:base-directory and :publishing-directory),
like:

,----
| (setq org-publish-project-alist
|       (list
|        '("foo" . (:base-directory "~/doc/foo/" ...
`----

When directories are given this way and ORG-PUBLISH-UPDATE-TIMESTAMP
uses the touch command to update the timestamp, it doesn't work because
Emacs should expand the ~/ into the home directory via EXPAND-FILE-NAME.

See the attached patch, Carsten please include this, thanks.