I was seeing error messages like: java.lang.ClassCastExeption: ArrayList at myCollecton.add ... i.e. It was creating a new ArrayList, then trying to add it into the parent collection instead of using the parent collection as a collection. I tracked the problem down to where the ValueList always created a new ArrayList. Avoiding constructing of the ValueList meant it uses my collection as a collection. NOTE: This was a generic (it checks the types on add hence the ClassCast) custom collection. View the original post : http://www.jboss.com/index.html?module=bb&op=viewtopic&p=3977238#... Reply to the post : http://www.jboss.com/index.html?module=bb&op=posting&mode=reply&a...