The us-core extension profiles have non-conformant element ids in them.

For example, us-core-race has

id: "Extension.extension:ombCategory.valueCoding"

which should be

id: "Extension.extension:ombCategory.value[x]:valueCoding"

Also, an additional differential element is needed at:

id: "Extension.extension:ombCategory.value[x]"

{{}} to limit the allowed value to Coding.

See http://hl7.org/fhir/elementdefinition.html#id and http://hl7.org/fhir/elementdefinition.html#typesx