I made an experiment as shown in the attachement: while using replace.py with the mentioned page in enwiki the problem really exists, another page from huwiki (default lang) may be well treated. So the problem is site-specific.
See the bug ( http://toolserver.org/~pywikipedia/b3427930 ) -- the problem is that 'nomad' once was an interwiki key, but it no longer is. Therefore, it should be removed from the 'known families' list - the problem is that Page('en', 'nomad:blah') was interpreted as Page(getSite('en', 'nomad'), 'blah'), which is incorrect.