Please run the following test example:

import java.beans.*;
import javax.swing.SwingContainer;

public class SwingContainerTest {
    
    @SwingContainer(true)
    public class Base {
        protected int x;
        @BeanProperty(description = "TEST", expert = true)
        public int getX() { return x; }
        public void setX(int v) { x = v; }
    }
    
    public class Child extends Base {}
    
    private static void Test(Class<?> c) throws IntrospectionException {
        
        System.out.println("test " + c.getSimpleName() + ":");
        BeanInfo i = Introspector.getBeanInfo(c, Object.class);
        PropertyDescriptor pds[] = i.getPropertyDescriptors();
        for (PropertyDescriptor d: pds) {
            System.out.println(d.getShortDescription() +
                    " property, isExpert = " + d.isExpert());
        }
        
        System.out.println("isContainer = " + i.getBeanDescriptor().getValue("isContainer") + "\n");
    }
    
    public static void main(String[] args) throws IntrospectionException {
        Test(Base.class);
        Test(Child.class);
    }
}

Output (JDK9 b77, Win 7):

test Base:
TEST property, isExpert = true
isContainer = true

test Child:
TEST property, isExpert = true
isContainer = null

so the property info was inherited, the container's - was not.