Adding a site to a network gets "wordpress" in paths and URLs

I successfully enabled the Network feature on my 3.0.1 install, however I get the following strange results when I try to add a site.

1) I add a site with a site address of mydomain/fr

Result, a site is created with the following settings:
Path mydomainwordpressfr/
SiteURL mydomainwordpressfr/
Home mydomainwordpressfr/
Fileupload URLmydomainwordpressde/files

Needless to say, none of the urls work.
Where is that “wordpress” string coming from? Why did it eat my “/”?