We have an OrderedSet which basically is a Set allowing index based access with the List interface (or a List with additional Set semantics). The implemented looks like this:

public class OrderedSet<E> extends ArrayList<E> implements Set<E> {
   ... implementation itself is not relevant for this test case...
}

When such an implementation is used with a List property

        @Valid
	public List<...> getDataAsList() // return instance of OrderedSet

we do get the expected results:

dataAsList[42]....

if something is invalid.

However if you use it with a Set property

	@Valid
	public Set<...> getDataAsSet() // return instance of OrderedSet

the index based access is no longer supported and we only get

dataAsSet[]....

Please note that both versions returned an index in 5.4.2.