Failure to unmarshal standard objects

I'm getting this error while unmarshaling metadata from my developer org:
Unexpected element. Parser was expecting element 'http://soap.sforce.com/2006/04/metadata:sorted' but found 'http://soap.sforce.com/2006/04/metadata:restrictedPicklist'

The specific object in question is Contract. I'm using the metadata WSDL generated from the same dev org using the same version of Force WSC. I've also been encountering this with older versions (at least as far back as 29.0) and with other orgs. The files haven't been modified in any way.