Error: Prefix [foo] of the QName [foo:states] is not bound in this context.

I am trying to write out a WPS request with an embedded WFS request but even though I define the namespace in namespacePrefixes, JSONIX is complaining that it's not set:

```
                    this.context = new Jsonix.Context([
                            XLink_1_0,
                            OWS_1_1_0,
                            Filter_1_1_0,
                            OWS_1_0_0,
                            SMIL_2_0,
                            SMIL_2_0_Language,
                            GML_3_1_1,
                            WFS_1_1_0,
                            WPS_1_0_0
                        ], {
                        namespacePrefixes : {
                            'http://foo': 'foo',
                            'http://www.w3.org/1999/xlink' : 'xlink',
                            'http://www.opengis.net/wps/1.0.0' : 'wps',
                            'http://www.opengis.net/ows/1.1' : 'ows'
                        }
                    });
```

JSON config:

```
{"name":{"localPart":"Execute","namespaceURI":"http://www.opengis.net/wps/1.0.0"},"value":{"service":"WPS","version":"1.0.0","identifier":{"value":"vec:FeatureClassStats"},"responseForm":{"rawDataOutput":{"identifier":{"value":"results"}}},"dataInputs":{"input":[{"identifier":{"value":"features"},"reference":{"method":"POST","mimeType":"text/xml","href":"http://geoserver/wfs","body":{"content":[{"name":{"namespaceURI":"http://www.opengis.net/wfs","localPart":"GetFeature"},"value":{"outputFormat":"GML2","service":"WFS","version":"1.1.0","query":[{"typeName":["foo:states"]}]}}]}}},{"identifier":{"value":"attribute"},"data":{"literalData":{"value":"POPULATION"}}},{"identifier":{"value":"classes"},"data":{"literalData":{"value":10}}},{"identifier":{"value":"method"},"data":{"literalData":{"value":"EQUAL_INTERVAL"}}},{"identifier":{"value":"stats"},"data":{"literalData":{"value":"mean"}}}]}}}
```