This is what is happening:
1º You have a BeanServiceImpl for example:
2º Create a java interface AnotherService (for instance)
3º Add a Reference with the tooling. Make Drag and Drop from the Core Reference palette to the main area.
4º Select the AnotherService interface
5º In the BeanServiceImpl click on CreateComponent Reference
6º Select AnotherService
Then in the Design view you do not see any error, but in the source view there is an error. See this is an example of a switchyard.xml
There is an error on this line:
cvc-complex-type.4: Attribute 'promote' must appear on element 'sca:reference'.