More Manila stuff: sitePref.set funkiness

So I’m having problems setting site prefs from my application. I was going to add a quick feature to allow managing editors to change the tagline of their site from within Manila Envelope, but I can’t get sitePref.set to work–it either complains about something not being a valid address or responds “true” without doing anything. I’ve put a detailed description on the XMLRPC discussion site.