Problem with PsiReferenceContributor in Java annotation strings

Hi,

I am trying to write a IntelliJ IDEA plugin for http://mapstruct.org/ the plugin should provide support for auto-completion and referencing the properties from the @Mapping annotation to the appropriate classes. In order to do that I am writing my own PsiReferenceContributor and implementing a resolve method appropriately. To better describe my problem, I'll write some code (the plugin will be open source in any case).

We have the following class:

public class Something { 
    private String field; 

    public String getField() {
        return field;
    }

    public void setField(String field) {
        this.field = field;
    }
}

public class SomethingElse { 
    private String anotherField; 

    public String getAnotherField() {
        return field;
    }

    public void setAnotherField(String anotherField) {
        this.anotherField = anotherField;
    }
}

I have the following Mapper 

public interface MyMapper {

    @Mapping(target = "field", source = "anotherField")
    Something map(SomethingElse source);
}

The value "field" resolves to the getField() method from Something and "anotherField` resolves to the method setAnotherField(String anotherField) from SomethingElse. Go To Declaration works correctly. However, when I want to Find Usages from the referenced methods the strings are not found, when I want to rename the methods in my PsiReferenceBase is not invoked, the strings are also not highlighted.

The resolve method for target looks like:

public PsiElement resolve() {
    PsiClass returnClass = getRelevantClass();
    String value = getValue();
    if ( returnClass == null || value.isEmpty() ) {
        return null;
    }
    PsiMethod[] methods = returnClass.findMethodsByName( "set" + Strings.capitalize( value ), true );

    return methods.length == 0 ? null : methods[0];
}

And for the source it looks like:

public PsiElement resolve() {
    PsiClass sourceClass = getRelevantClass();
    String value = getValue();
    if ( sourceClass == null || value.isEmpty()) {
        return null;
    }
    PsiMethod[] methods = sourceClass.findMethodsByName( "get" + Strings.capitalize( value ), true );

    return methods.length == 0 ? null : methods[0];
}

However, if I change resolve methods to (similar as the resolve for the TestNg DataProvider and the JUnit 5 MethodSource):

public PsiElement resolve() {
    PsiClass sourceClass = getRelevantClass();
    String value = getValue();
    if ( sourceClass == null || value.isEmpty()) {
        return null;
    }
    PsiMethod[] methods = sourceClass.findMethodsByName( value, true );

    return methods.length == 0 ? null : methods[0];
}

And the mapping to (this is not a valid MapStruct mapping):

public interface MyMapper {

    @Mapping(target = "setField", source = "getAnotherField")
    Something map(SomethingElse source);
}

Then everything works correctly. When I do Find Usages on the methods, then they are found, renaming works as well and the strings are highlighted. 

I really do not understand what I am doing wrong. Why is the first approach not working?