Sidebar styles broken when `pageConfig` is left out of config

[marshallswain]

{
    "siteDefaults": {
        "static":"theme/static",
        "templates": "theme/templates"
    },
    "sites": {
        "guides":{
            "glob": {
                "pattern": "_docs/guides/**/*.{js,md}"
            },
            // Leaving this out results in a poorly-styled sidebar & page
            "pageConfig": {"page":"guides"}, 
            "parent": "Guides",
            "dest":"guides"
        }
    }
}

Without pageConfig in documentjs.json:

VS

With pageConfig in documentjs.json:

[marshallswain]

Looks like this might be more related to the .less styles. I'm not sure if this is explicitly documented, yet, so I'm leaving it open.