@Sortable annotation always sorts by the parent properties

import groovy.transform.Sortable
import org.junit.Test

class SortableTest {

 @Sortable(includes = ["num"])
 class SortableClass{
 Integer num
 }

 @Sortable(includeSuperProperties = false, includes = ["str"])
 class SortableChild extends SortableClass {
 String str
 }

 @Test
 void test(){
 List<SortableChild> unsortedList = [new SortableChild([str: "B", num: 1]), new SortableChild([str: "A", num: 2])]
 List<SortableChild> sortedList = unsortedList.toSorted()
 assert sortedList[0].str == "A" //Fails here
 }
}