I see this question is pretty old and I don't know if you have found a solution by now, but just in case, this is what I have found will resolve:
1) In the Solution Explorer, under the Service References folder, right-click the service reference name with the issue and select 'Configure Service Reference'.
2) The Service Reference Settings window will appear. Uncheck the box labeled 'Reuse types in referenced assemblies' and click the OK button.
3) Rebuild the project.
After rebuilding, the warning should disappear.