Background info:  I've been working on a process to upload conformance resources from the US Core package.tgz file.  The target FHIR server is based on HAPI FHIR 5.1.0, and has basic FHIR validation enabled (but terminology checks disabled).

The FHIR resource types being extracted from the package.tgz file and uploaded to the server are:  CodeSystem, ValueSet, ConceptMap, SearchParameter, OperationDefinition, StructureDefinition, and CapabilityStatement.

The server's FHIR validator reports errors in several of the resource files contained in the package.tgz file for US Core STU2 (for FHIR R3), downloadable here: 

http://hl7.org/implement/standards/fhir/us/core/STU2/downloads.html

Summary of validation errors, by filename:

• package/ValueSet-us-core-medication-codes.json
  Profile reference 'http://hl7.org/fhir/StructureDefinition/valueset-shareable-definition' could not be resolved, so has not been checked
• package/ValueSet-us-core-problem.json
  Profile reference 'http://hl7.org/fhir/StructureDefinition/valueset-shareable-definition' could not be resolved, so has not been checked
• package/ValueSet-us-core-substance.json
  Profile reference 'http://hl7.org/fhir/StructureDefinition/valueset-shareable-definition' could not be resolved, so has not been checked
• package/ValueSet-us-core-procedure-icd10pcs.json
  Profile reference 'http://hl7.org/fhir/StructureDefinition/valueset-shareable-definition' could not be resolved, so has not been checked
• package/ValueSet-us-core-procedure-code.json
  Profile reference 'http://hl7.org/fhir/StructureDefinition/valueset-shareable-definition' could not be resolved, so has not been checked
• package/ValueSet-us-core-observation-ccdasmokingstatus.json
  Profile reference 'http://hl7.org/fhir/StructureDefinition/valueset-shareable-definition' could not be resolved, so has not been checked
• package/StructureDefinition-us-core-direct.json
  The generated snapshot has a different number of elements 6 that the originally provided snapshot 5
• package/StructureDefinition-us-core-birthsex.json
  The generated snapshot has a different number of elements 6 that the originally provided snapshot 5
• package/StructureDefinition-us-core-race.json
  The generated snapshot has a different number of elements 35 that the originally provided snapshot 20
• package/StructureDefinition-us-core-ethnicity.json
  The generated snapshot has a different number of elements 35 that the originally provided snapshot 20
• package/StructureDefinition-us-core-profile-link.json
  The generated snapshot has a different number of elements 6 that the originally provided snapshot 5
• package/StructureDefinition-us-core-device.json
  Profile http://hl7.org/fhir/StructureDefinition/CapabilityStatement, Element 'CapabilityStatement.acceptUnknown': minimum required = 1, but only found 0

(The above list includes validation errors, but not warnings.)

Notes:

It looks like valueset-shareable-definition was present in the 2015May version of the FHIR spec, but was replaced by shareablevalueset in the 2015Sep version.

[http://hl7.org/fhir/2015May/valueset-shareable-definition.html
] http://hl7.org/fhir/2015Sep/shareablevalueset.html

The attached file contains more complete (JSON) validator output for these cases.

If possible, please remedy these issues in a technical correction to the US Core STU2 IG.