Rewriting HOST+URI does not work

Hi, I just tested this one:

when HTTP_REQUEST {
    if { [string tolower [HTTP::uri]] starts_with "/webfront" } {
        set subd [getfield [HTTP::host] ".domain.com" 1]
         log local0. "subd: <$subd>"
        if { $subd contains "-dmz" } {
            set subd [string map {"-dmz" ""} $subd]
        }
        HTTP::header replace Host "${subd}-webfront.domain.com"
        HTTP::uri [string map {"/webfront" ""} [HTTP::uri]]
    }
}

Thanks, Stephan