${uid._lowerCase} is not always properly interpreted

I have set the following property:

    xwiki.authentication.ldap.userPageName=${uid._lowerCase}

which I think should create  a profile page as the user name (cn in my case, as I an using OpenLDAP) in lower case.

Instead profile pages are named XWiki.${uid_lowerCase}. I guess that is because "special characters" like . are stripped from the user page name before doing the substitution of the userPageName property, not afterwards.