I guess there is bug somewhere in the wiki: I just created a page (http://our.umbraco.org/wiki/user-groups/europe/italy) and it appears twice in the list of sub-pages of Europe.

Actualluy I created it twice, one with the correct title and another with the "the page with title italy is not found", then I renamed it, and think now I've got two pages with the same url/title.