Problem of Generic List with Jettison Driver

I am using xstream 1.3.1 with Jettison 1.1 to generate json. I have a generic list with a structure like such

import xxx.xxx.A;

List<A> aList;

XStream xstream = new XStream(new JettisonMappedXmlDriver());
xstream.setMode(XStream.NO_REFERENCES);
String s=xstream.toXML(product);

It will generate something like below

["List":["xxx.xxx.A":[FIRST,SECOND,...]]

I switch to their internal JsonHierarchicalStreamDriver and the "xxx.xxx.A" level goes away

["List":[FIRST,SECOND,...]]

I am not sure whether it is the problem of xstream or jettison. But I am not familiar with Jettison enough to test it. Hopefully this is useful information for someone.