Subdirectory provisioned sites with periods in them do not work

When we provision MultiSite sites with a . in the name (subdirectory mode), the sites cannot be viewed, and a version of the main blog without CSS is shown instead.

For example, if the main site's URL is and we create, the newly-created site cannot be viewed and instead the site for is shown without CSS.

If we create simply, the newly-created site can be viewed and worked on as normal.

Does anyone have an idea how this can be fixed? Our provisioning module for MultiSites only supports using full domain names. It sounds like it might be something with .htaccess or something.

Thanks in advance!